Date: Tue, 29 Oct 2013 00:48:32 +0400 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Allan Jude <freebsd@allanjude.com> Cc: freebsd-current@freebsd.org Subject: Re: ZFS txg implementation flaw Message-ID: <20131028204832.GA66537@zxy.spb.ru> In-Reply-To: <526EACB4.9030906@allanjude.com> References: <20131028092844.GA24997@zxy.spb.ru> <0F1D571E-2806-4392-A5EC-BE66A3C92BF7@gmail.com> <20131028181631.GV63359@zxy.spb.ru> <526EACB4.9030906@allanjude.com>
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On Mon, Oct 28, 2013 at 02:28:04PM -0400, Allan Jude wrote: > On 2013-10-28 14:16, Slawa Olhovchenkov wrote: > > On Mon, Oct 28, 2013 at 10:45:02AM -0700, aurfalien wrote: > > > >> On Oct 28, 2013, at 2:28 AM, Slawa Olhovchenkov wrote: > >> > >>> I can be wrong. > >>> As I see ZFS cretate seperate thread for earch txg writing. > >>> Also for writing to L2ARC. > >>> As result -- up to several thousands threads created and destoyed per > >>> second. And hundreds thousands page allocations, zeroing, maping > >>> unmaping and freeing per seconds. Very high overhead. > >>> > >>> In systat -vmstat I see totfr up to 600000, prcfr up to 200000. > >>> > >>> Estimated overhead -- 30% of system time. > >>> > >>> Can anybody implement thread and page pool for txg? > >> Would lowering vfs.zfs.txg.timeout be a way to tame or mitigate this? > > vfs.zfs.txg.timeout: 5 > > > > Only x5 lowering (less in real case with burst writing). And more fragmentation on writing and etc. > > _______________________________________________ > > freebsd-current@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-current > > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" > >From my understanding, increasing the timeout so you are doing fewer > transaction groups, would actually be the way to increase performance, > at the cost of 'bursty' writing and the associated uneven latency. This (increasing the timeout) is dramaticaly decreasing read performance by very high IO burst.home | help
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