Date: Wed, 5 Nov 2003 02:09:37 -0600 From: Alan Cox <alc@cs.rice.edu> To: Vivek Pai <vivek@CS.Princeton.EDU> Cc: freebsd-hackers@freebsd.org Subject: Re: Update: Debox sendfile modifications Message-ID: <20031105080937.GA9687@cs.rice.edu> In-Reply-To: <3FA897E7.5020103@cs.princeton.edu> References: <1066789354.21430.39.camel@boxster.onthenet.com.au> <20031022082953.GA69506@rot13.obsecurity.org> <1066816287.25609.34.camel@boxster.onthenet.com.au> <20031022095754.GA70026@rot13.obsecurity.org> <xzpk76sc425.fsf@dwp.des.no> <1067183332.3f9bece4c0cf4@webmail.cs.princeton.edu> <3FA2C43E.3030204@cs.princeton.edu> <3FA7EF77.5010808@cs.princeton.edu> <20031104221455.I9997@odysseus.silby.com> <3FA897E7.5020103@cs.princeton.edu>
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On Wed, Nov 05, 2003 at 01:25:43AM -0500, Vivek Pai wrote: > Mike Silbersack wrote: > >On Tue, 4 Nov 2003, Vivek Pai wrote: > >>The one other aspect of this is that sf_bufs mappings are maintained for > >>a configurable amount of time, reducing the number of TLB ops. You can > >>specify the parameter for how long, ranging from -1 (no coalescing at > >>all), 0 (coalesce, but free immediately after last holder release), to > >>any other time. Obviously, any value above 0 will increase the amount of > >>wired memory at any given point in time, but it's configurable. > > > >Ah, I missed that point. Did your testing show the caching part of the > >functionality to be significant? > > I think it buys us a small gain (a few percent) under static-content > workloads, and a little less under SpecWeb99, where more time is spent > in dynamic content. However, it's almost free - the additional > complexity beyond just coalescing is hooking into the timer to free > unused mappings. I think it's reasonable to expect a more pronounced effect on i386 SMP. In order to maintain TLB coherence, we issue two interprocessor interrupts _per_page_ transmitted by sendfile(2). Alan
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