Messages in this thread | | | Date | Sun, 02 Jul 2006 03:40:23 +1000 | From | Nick Piggin <> | Subject | Re: [patch 0/2] sLeAZY FPU feature |
| |
Arjan van de Ven wrote: > Hi, > > the two patches in this series (the x86-64 on by me, the i386 one by > Chuck Ebbert) change how the lazy fpu feature works. In the current > situation, we are 100% lazy, meaning that after every context switch, > the application takes a trap on the first FPU use, which then restores > the FPU context. > > The sLeAZY FPU patch changes this behavior; if a process has used the > FPU for 5 stints at a row, the behavior becomes proactive and the FPU > context is restored during the regular context switch already. This > means we can avoid the trap. > > The underlying assumption is that if a process uses 5 times consecutive, > it's likely to do it the 6th and later times as well (eg it's not a > one-off behavior). > > There is a limit built in; this proactive behavior resets after 255 > times, so that when a process is long lived and chances behavior, it'll > still get the right behavior (for performance) after some time. > > Chuck measured a +/- 0.4% performance gain, and my experiments show a > similar improvement.
What sort of test? Any idea of the results for a best case microbenchmark (something like two threads ping-pong a couple of futexes between them, in between doing a single FPU op)
-- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |