[Ksummit-discuss] [TOPIC] Application performance: regressions, controlling preemption
Chris Mason
clm at fb.com
Mon May 12 14:32:27 UTC 2014
Hi everyone,
We're in the middle of upgrading the tiers here from older kernels
(2.6.38, 3.2) into 3.10 and higher.
I've been doing this upgrade game for a number of years now, with
different business cards taped to my forehead and with different target
workloads.
The result is always the same...if I'm really lucky the system isn't
slower, but usually I'm left with a steaming pile of 10-30% regressions.
The KS dates should put us right at the end of our regression hunt, I
can talk through the main problems we hit, how (if) we fixed them and
hopefully offer tests to keep them from coming back.
We've split the tiers up between Josef Bacik, Jens Axboe, myself and a
few others. I'd nominate Josef and Jens to come share their findings as
well.
Another topic here is controlling preemption from userland without
needing to go full real time. CPU intensive in-memory databases are
leaving a ton of performance on the floor in context switches. I'm
hoping to experiment with better preemption controls and the userland
RCU project to improve things.
-chris
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