From mboxrd@z Thu Jan 1 00:00:00 1970 From: Con Kolivas Subject: Re: [ck] Re: [PATCH] mm: yield during swap prefetching Date: Thu, 9 Mar 2006 00:36:48 +1100 References: <200603081013.44678.kernel@kolivas.org> <20060307152636.1324a5b5.akpm@osdl.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200603090036.49915.kernel@kolivas.org> Sender: owner-linux-mm@kvack.org Return-Path: To: ck@vds.kolivas.org Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ingo Molnar List-ID: cc'ing Ingo... On Wednesday 08 March 2006 10:32, Con Kolivas wrote: > Andrew Morton writes: > > Con Kolivas wrote: > >> Swap prefetching doesn't use very much cpu but spends a lot of time > >> waiting on disk in uninterruptible sleep. This means it won't get > >> preempted often even at a low nice level since it is seen as sleeping > >> most of the time. We want to minimise its cpu impact so yield where > >> possible. > >> > >> Signed-off-by: Con Kolivas > >> --- > >> mm/swap_prefetch.c | 1 + > >> 1 file changed, 1 insertion(+) > >> > >> Index: linux-2.6.15-ck5/mm/swap_prefetch.c > >> =================================================================== > >> --- linux-2.6.15-ck5.orig/mm/swap_prefetch.c 2006-03-02 > >> 14:00:46.000000000 +1100 +++ > >> linux-2.6.15-ck5/mm/swap_prefetch.c 2006-03-08 08:49:32.000000000 +1100 > >> @@ -421,6 +421,7 @@ static enum trickle_return trickle_swap( > >> > >> if (trickle_swap_cache_async(swp_entry, node) == TRICKLE_DELAY) > >> break; > >> + yield(); > >> } > >> > >> if (sp_stat.prefetched_pages) { > > > > yield() really sucks if there are a lot of runnable tasks. And the > > amount of CPU which that thread uses isn't likely to matter anyway. > > > > I think it'd be better to just not do this. Perhaps alter the thread's > > static priority instead? Does the scheduler have a knob which can be > > used to disable a tasks's dynamic priority boost heuristic? > > We do have SCHED_BATCH but even that doesn't really have the desired > effect. I know how much yield sucks and I actually want it to suck as much > as yield does. Thinking some more on this I wonder if SCHED_BATCH isn't a strong enough scheduling hint if it's not suitable for such an application. Ingo do you think we could make SCHED_BATCH tasks always wake up on the expired array? Cheers, Con -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org