Date: Sun, 29 Aug 2010 05:38:05 -0400 From: jhell <jhell@DataIX.net> To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: freebsd-current@freebsd.org, Artem Belevich <fbsdlist@src.cx>, Martin Matuska <mm@freebsd.org>, Andriy Gapon <avg@icyb.net.ua> Subject: Re: [CFT] Improved ZFS metaslab code (faster write speed) Message-ID: <4C7A2A7D.5040007@DataIX.net> In-Reply-To: <20100828092602.GG2077@garage.freebsd.pl> 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> <4C78D0EE.6040708@DataIX.net> <20100828092602.GG2077@garage.freebsd.pl>
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On 08/28/2010 05:26, Pawel Jakub Dawidek wrote:
> On Sat, Aug 28, 2010 at 05:03:42AM -0400, jhell wrote:
>> 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.
>
> Could you include the following patch to your testing:
>
> http://people.freebsd.org/~pjd/patches/arc.c.9.patch
>
Sure thing. Adding it now.
--
jhell,v
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