Willy Tarreau <[email protected]> writes:
> What is your workload ?
There are two separate workloads that are affected by this issue:
- one is a pretty typical whole-distribution build, which gets 1.5x to 2x
slower with v2.6.32.60
- the other is a code simulator, which is basically a bunch of processes
communicating together using POSIX message queues (mq_timedsend() and
mq_timedreceive()). It runs approximately 10x slower, but doesn't seem
to use more CPU, it just sits there doing pretty much nothing.
I managed to narrow the second workload down to a single test case, which
runs in approximately 0.7s in v2.6.32.59 and 8s (!) in v2.6.32.60. Having
a simple test case allowed me to do a full bisection in a test VM, and it
ends on commit 61b76840ddee647c0c223365378c3f394355b7d7 ("time: Avoid
making adjustments if we haven't accumulated anything").
And indeed, if I revert this commit from v2.6.32.60 then everything is
back to normal.
Looking at the history of the corresponding source file, ec145babe754f
("time: Fix timeekeping_get_ns overflow on 32bit systems") might be
similar to what I'm seeing: timers not firing as they should on 32-bit
systems. I'm using a 32-bit kernel with an older 32-bit userspace from
Debian etch, in KVM.
CC'ing John, who probably knows more about this than we do.
Thanks,
-r
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