Date: Sat, 28 Aug 2010 05:03:42 -0400 From: jhell <jhell@DataIX.net> To: Andriy Gapon <avg@icyb.net.ua> Cc: freebsd-current@freebsd.org, Artem Belevich <fbsdlist@src.cx>, Martin Matuska <mm@freebsd.org> Subject: Re: [CFT] Improved ZFS metaslab code (faster write speed) Message-ID: <4C78D0EE.6040708@DataIX.net> In-Reply-To: <4C78C6C3.1010005@icyb.net.ua> References: <4C713EF5.8080402@FreeBSD.org> <AANLkTi=8x1EenWyqGz6AQWKDUq5JiMJbX_jbVbX43DKx@mail.gmail.com> <4C714FC0.90005@FreeBSD.org> <AANLkTim_BH4WrQUY-X491c%2BfLaP2FKMcS1k-DN5tLG-9@mail.gmail.com> <20100828081917.ee931f7f.nork@FreeBSD.org> <AANLkTi=hbL3wfTvmfBhPkpJ7orh_WuhagGPoXaS_hcTW@mail.gmail.com> <4C78655C.3010200@DataIX.net> <4C78C6C3.1010005@icyb.net.ua>
next in thread | previous in thread | raw e-mail | index | archive | help
On 08/28/2010 04:20, Andriy Gapon wrote:
> on 28/08/2010 04:24 jhell said the following:
>> The modified patch from avg@ (portion patch) is:
>>
>> #ifdef _KERNEL
>> if (arc_reclaim_needed()) {
>> needfree = 0;
>> wakeup(&needfree);
>> }
>> #endif
>>
>> I still moved that down to below _KERNEL for the obvious reasons. But
>> when I was using the original patch with if (needfree) I noticed a
>> performance degradation after ~12 hours of use with and without UMA
>> turned on. So far with ~48 hours of testing with the top half of that
>> being with the above change, I have not seen more degradation of
>
> This is quite unexpected.
> needfree should be checked as the very first thing in arc_reclaim_needed()
> [unless you have patched it locally]. So if needfree is 1 then
> arc_reclaim_needed() should also return 1. But the converse is not true,
> arc_reclaim_needed() may return 1 even if needfree is zero.
>
> So if your testing results are conclusive then it must mean that some extra
> wakeups on needfree are needed. I.e. needfree is zero, so there shouldn't be
> anything waiting on it (see arc_lowmem) and no notification should be needed,
> but issuing somehow does make difference,
> Hmm...
>
I will look further into this and see if I can throw a counter around it
or some printf's so I can at least log what its doing in both instances.
I thought the very same thing you said above when I saw your patch for
that and was astounded at the results that were returned from it. So in
short testing I reverted it back quickly to see if that was the cause of
the problem and sure enough everything resumed to the way it was before.
Anyway thanks for the reply. I will get back to you if I see anything
cool arise from this.
Regards,
--
jhell,v
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4C78D0EE.6040708>