Messages in this thread | | | Subject | Re: PROBLEM: relay - stale data copied to user space | From | Martin Peschke <> | Date | Thu, 19 Mar 2009 18:50:40 +0100 |
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On Wed, 2009-03-18 at 23:19 -0500, Tom Zanussi wrote: > On Wed, 2009-03-18 at 16:07 +0100, Martin Peschke wrote > > This is my theory: > > Timing matters. It's a race caused by improper protection of critical > > sections in a producer-consumer scenario. A bug in the bookkeeping > > allows a reader to read at a position that is just being written to. > > > > It does look consistent with a reader reading an event that's been > reserved but not yet written, or partially written e.g. if an event > being written on one cpu was read by another before the first one > finished.
So this is part of relay's design, and it's up to user space to make sure that reader and writer are on the same CPU?
> Can you see if the below patch to blktrace userspace helps?
It appears to fix it. I will give it more testing in a larger environment.
> Or failing that, explicitly using gettid() in place of getpid() in > sched_setaffinity(). Or, failing that, you had mentioned previously > that you would try to reproduce the problem on your laptop - were you > able to do that? If so, it would help in debugging it further...
This didn't work out. But then, it's a single-CPU machine.
Thanks, Martin
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