Older blog entries for dreier (starting at number 35)

Quit Today

I’m a slow blogger.  I’ve been meaning to post some thoughts about Greg’s [in]famous LPC keynote for a while now, but it’s taken me nearly two months to get to it.  I’ll start off by saying the same thing that I told Greg in person: I don’t think it was an appropriate setting for for Greg to single out Canonical for criticism.  It doesn’t matter who started it, it doesn’t matter what the merits of a particular argument are, and it doesn’t make sense for Greg to say he was not speaking as a Novell employee, since he is a Novell employee.  But I don’t really want to get drawn into that debate.

The slide that really stuck with me from Greg’s talk is the one from the conclusion that says, “Developers who are not allowed to contribute to Linux should change jobs.”  In the text for the talk, Greg writes, “The solution, quit and go work for one of the companies that allow you to do this!”  And I have to agree with this advice, because I think contributing to free software is in the rational self-interest of nearly any software developer.

When I started in this game about a decade ago, I was a typical Silicon Valley “senior software engineer” type: bright guy, knows how to code, decent resume.  I had a circle of people who I had worked with who knew me, but if I went for a job interview, the people interviewing me were usually meeting me for the first time.  But I was fortunate enough to end up in a job where I was working on open source InfiniBand drivers for Linux, and ended up becoming the Linux kernel InfiniBand/RDMA maintainer.  I should mention that it wasn’t a question of being “allowed” to contribute to Linux — I knew that InfiniBand needed open-source Linux support, and I didn’t listen to anyone who said “no.”

It has been great fun and very rewarding to build the Linux InfiniBand stack, but I just want to focus on the venal career side of this.  And the point is that tons of people know me now.  They know what I can do in terms of kernel coding, and maybe more importantly, they can see how I do it, how I respond to bug reports and how I handle the techno-diplomacy of collaborating on mailing ists.  And this has had a definite effect on my career.  I’m not just YASSE (yet another senior software engineer); I get calls from people I’ve never met offering me really interesting and very senior jobs.  And when hiring, I am certainly much more comfortable with candidates who have a visible history of contribution to open source, simply because I can see both their technical and social approach to development.

I do think that the contributions that have this value to individuals can be beyond Greg’s kernel/gcc/binutils/glibc/X view of the “Linux ecosystem.”  If people have done substantial work on, say, bzr or the Ubuntu installer, that’s still something I can go look at when I’m thinking about hiring them.  Of course, making contributions to a highly visible project carries more weight than contributing to a less visible project, but on the other hand, maybe there’s more room to shine in a project with a smaller community of developers.

Finally, Greg’s advice to “quit” made me think of a book from a few years ago, Die Broke that has as one of its main pieces of advice to “quit today.”  However, this advice is just a provocative way of saying that workers should be conscious of the fact that their employer probably has little to no real loyalty to employees, and so individual workers should focus on their own best interests, rather than what might be best for their employer.  And I think that metaphorical view applies just as well to Greg’s advice to quit: if you feel that you can’t contribute to open source in your present job, what’s stopping you?  Do you really need to change employers to start contributing, or can you just tweak your current job?  What will happen if you tell your manager, “Open source is good for our business for reasons X, Y and Z, and also it’s important to me for my career development, so can we come up with a way for me to start contributing?”

Syndicated 2008-10-29 17:54:14 from Roland's Blog

It takes all kinds

Seen at the library: a dude with a stack of Cathy books on the table in front of him, barely controlling his laughter as he reads My Granddaughter Has Fleas!!

Syndicated 2008-05-20 22:30:02 from Roland's Blog


I just saw a dude order a 4-shot red eye.

Syndicated 2008-04-15 21:21:48 from Roland's Blog

Lies, d… oh, forget it

I noticed the recent blog post “Cisco Set to Dominate Linux Market?” (which lwn.net also linked), but the part that caught my eye was:

According to a recent Linux Foundation study, Cisco is already contributing to Linux and currently represents 0.5 percent of changes (which is a good number). I would expect that with the AXP in the market, Cisco’s contribution rate will go up.

Now, I don’t work on AXP or anything related to ISRs, so I have no idea what those groups plan to do with respect to Linux, but it was somewhat amusing to see the Linux Foundation report cited to show how much work CIsco does on the kernel.

This isn’t the first time I’ve seen this study cited to show what a kernel development powerhouse Cisco is.  In the report, Cisco is credited with 442 commits to the kernel; however, more than 400 of of those commits are mine, and about 30 are Don Fry maintaining the pcnet32 net driver.  So if you take away my work on InfiniBand/RDMA, Cisco’s contributions to the Linux kernel are pretty minimal.

I’m not sure if I have much of a point except that I wish we really did have more than one or two isolated developers at Cisco really engaged with the upstream kernel.

Syndicated 2008-04-12 03:45:39 from Roland's Blog

He who divides and shares is left with the best share

I’ve been talking to a lot of people about the “iWARP port sharing problem” lately, so I thought it might be a good idea to write a quick summary to point at and bring new people up to speed without constantly repeating myself.

To start with, iWARP is an RDMA (remote direct memory access) protocol that runs over TCP (or conceivably SCTP or any other stream protocol). It was defined by the IETF rddp working group, and the standard is in RFC 5040 and later RFCs. So what’s so great about RDMA?

The rationale for RDMA is laid out in great detail in RFC 4297, but the basic idea is that allowing network messages to carry information about where they should be received and allowing the NIC to place the data directly in that buffer allows fundamentally better performance.

To take a concrete example, think of iSCSI: an initiator sends a bunch of SCSI commands to a target (probably queuing up multiple commands), and the target processes the commands, possibly out of order, and returns the responses to the initiator. Without RDMA (or at least, without “direct data placement,” which is pretty equivalent to RDMA), for each read that the initiator does, it has to receive the data from the target, look at which command the data corresponds to, and copy it into the buffer that the SCSI midlayer wants it in. With RDMA and the “iSCSI Extensions for RDMA” (iSER, which is RFC 5046), the target can send the data in response to a read command and have it placed directly in the receive buffer on the initiator, which saves the copy and uses 3x less memory bandwidth (which is huge if the data is running at 10Gb/sec). In the SCSI world, this is nothing particularly exciting: pretty much every Fibre Channel HBA in the world already does the equivalent thing. What’s cool about iWARP is that it allows similar optimizations for NFS (the IETF nfsv4 working group is defining a standard for NFS/RDMA, and kernel 2.6.24-rc1 already has the client side of this draft protocol merged) as well as other applications that we haven’t thought of yet.

The way that iWARP is implemented is that RDMA NICs handle the full iWARP protocol including TCP in hardware — yes, the dreaded “TCP offload engine.” This is crucial to the performance: if the network data isn’t processed to the point of knowing where to put it on the NIC’s side of the PCI bus, then the memory bandwidth savings of copy avoidance is lost. So while one can imagine an iWARP implementation with stateless NIC hardware using some super-fancy header splitting and chipset DMA engine tricks, it’s not clear that it will perform as well as current iWARP NICs do.

Now, in addition to handling TCP connections, iWARP NICs also have to act like normal NICs so that they can handle normal network traffic such as ARPs, pings or ssh logins. What this means is that some packets are received normally and passed up the standard network stack, while other packets that belong to iWARP connections are consumed by the NIC.

This is what leads to the “port sharing problem.” One application might do a normal bind() to accept TCP connections on port X. It might even let the kernel choose a port number for it. Then another application (possibly even the same application) does an iWARP bind and tells the iWARP NIC to accept TCP connections on the same port X. This might happen because two different applications do the bind and have no way of coordinating with each other, or it might happen because one application just passes 0 in the sin_port field of its bind requests, and the kernel chooses the same port for both the normal and iWARP bind(). Whatever the reason, the end result is not good: the NIC and the network stack are left fighting for the same packets, and someone has to lose.

The reason this is an issue is because the kernel’s network stack and iWARP stack have completely separate port allocators, so there is no way for applications to prevent port collisions from happening. The obvious solution is to have normal TCP and iWARP port numbers allocated from the same space.

Unfortunately, the Linux networking developers are not too interested in cooperating on this. It seems that some people have just decided that anyone who wants to use iWARP is wrong to want that (no matter how much better than the alternatives it is for that user’s app) and will just reflexively reject anything iWARP-related without trying to engage in constructive discussion. (Given that attitude, it’s rather ironic when the same people preach about open-mindedness and “thinking outside the box,” but let’s not get sidetracked…)

Given the current deadlock, the advice I’ve been giving to the various iWARP NIC companies is just to sell a lot of iWARP NICs and make the problem so big that we’re forced to find a solution. I don’t see any other way to force people to work together.

Syndicated 2007-11-06 19:15:21 from Roland's Blog

On social networks

With Google’s big OpenSocial announcement, I find myself thinking about social networking in general. I think I may be a generation or so too old to really “get it,” but I do use four social networking sites at least a little bit:

  • advogato: I’ve had an account there for quite a while, but the only thing I’ve done with it for years has been to syndicate this blog there. The theory of the certification network is very interesting, but it’s probably been five years since I’ve certified anyone or gotten a certification…
  • ohloh: I created an account and claimed all the committer identities I could there a few months ago, but too be honest I don’t see much reason to look at the site. Besides, I’m very unimpressed that they seem to have completely ignored all the research from advogato on how to compute scores and just hacked up something hokey. And they can’t even seem to keep their kernel git tree updated properly.
  • linkedin: I’ve had an account there for a while, and it seems like the most useful social networking site for what I want to do, which is really just to keep track of the email address of people I know and get back in touch with people I’ve lost touch with. I’ve even had one friend of a friend referred to me for a job opening, which I guess is exactly what the site is supposed to be for.
  • facebook: I recently created an account there for the same reason I use linkedin. Like I said before, I think I’m too old to get into all the widgets and movie quizzes and share my favorite music and buy fish for my aquarium and so on, but I do have friends who aren’t on linked in who are on facebook. And it is nice to get birthday reminders I guess.

If Google can open all this up so I have better control of my own information and don’t have to deal with three or four different sites all the time, that would be cool. But I doubt they can pull off anything so pro-consumer….

Syndicated 2007-11-01 18:17:13 from Roland's Blog

Materials from LinuxConf.eu RDMA tutorial (at last)

At long last, after several requests, I’ve posted the slides, notes, and client and server examples from the tutorial I gave at LinuxConf.eu 2007 in Cambridge back in September.  Hyper-observant readers will notice that the client program I posted does not match the listing in the notes I handed out; this is because I fixed a race condition in how completions are collected.

I’m not sure how useful all this is without me talking about it, but I guess every little bit helps.   And of course, if you have questions about RDMA or InfiniBand programming, come on over to the mailing list and fire away.

Syndicated 2007-10-10 21:38:24 from Roland's Blog

InfiniBand/RDMA in 2.6.23 and 2.6.24

With yesterday’s release of  kernel 2.6.23, I thought it might be a good time to look back at what significant changes are in 2.6.23, and what we have queued up for 2.6.24..

So first I looked at the kernel git log from the v2.6.22 tag to the v2.6.23 tag, and I was surprised to find that nothing really stood out.  We merged something like 158 patches that touched 123 files, but I couldn’t really find any headline-worthy new features in there.  There were just tons of fixes and cleanups all over, although mostly in the low-level hardware drivers.  For some reason, 2.6.23 was a pretty calm development cycle for InfiniBand and RDMA, which means that at least that part of 2.6.23 should be rock solid.

2.6.24 promises to be a somewhat more exciting release for us.  In my for-2.6.24 branch, in addition to the usual pile of fixes and cleanups, I have a couple of interesting changes queued up to merge as soon as Linus starts pulling things in:

  •  Sean Hefty’s quality-of-service support.  These changes allow administrators to configure the network to give different QoS parameters to different types of traffic (eg IPoIB, SRP, and so on).
  • A patch from me (based on Sean Hefty’s work) to handle  multiple P_Keys for userspace management applications.  This is one of the last pieces to make the InfiniBand stack support IB partitions fully.

Also, bonding support for IP-over-InfiniBand looks set to go in through Jeff Garzik’s tree.  This is something that I’ve been wanting to see for years now; the patches allow the standard bonding module to enslave IPoIB interfaces, which means that multiple IB ports can finally be used for IPoIB high-availability failover.  Moni Shoua and others did a lot of work and stuck with this for a long time, and the final set of patches turned out to be very clean and nice, so I’m really pleased to see this get merged.

Syndicated 2007-10-10 18:18:32 from Roland's Blog

Shape up or ship out

I know I’m not in the shape I once was, but it seems rather cruel of the Cantabrigians to send around huge signs on buses that say “Run, Fatboy, Run” when I go out for a morning jog.

Syndicated 2007-09-03 21:46:18 from Roland's Blog

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