Date: Mon, 03 Jan 2005 11:53:51 -0800 From: Nate Lawson <nate@root.org> To: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: ATA rman performance enhancement Message-ID: <41D9A2CF.30704@root.org> In-Reply-To: <41D99FBD.8070500@DeepCore.dk> References: <41D984A5.7010408@root.org> <41D99FBD.8070500@DeepCore.dk>
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Søren Schmidt wrote: > Nate Lawson wrote: > >> While doing some benchmarking of other code, I noticed that there were >> a lot of calls to rman_get_bustag/handle(). They weren't taking up >> much actual time since they're pretty lightweight but seemed to be >> unnecessary. >> >> I worked up the attached diff and benchmarked it. There are about >> 1000 calls a second to the rman routines without this patch and >> essentially none with it. It makes about a 1% difference in >> throughput under some IO loads. It is only for non-Promise or non-SII >> controllers right now since I didn't extend the initialization step to >> more than ata-pci.c. The same approach could be used for the other >> INW/OUTW calls as well but they're not in the fast path. I think it >> may make more of a difference with small reads. >> >> Feel free to test, cleanup, and commit. > > > I had something semilar to this once back when, but since HW got lots > faster I couldn't measure it anymore, but maybe things has changed... > > Anyhow it needs to be applied to ata-isa.c ata-card.c ata-cbus.c etc to > not break anything at least. Yes, I agree. I limited the change only to the IDX macros that were used in the fast path although it could apply to all of them. > I'll think about it and eventually do > something about it in ATA-mkIII if it really is mesureable again.. It is a minimal difference but with small transfers on a fast drive with a low-powered CPU, it's measurable. I made the same change a while back in acpi_timer.c since the resource is only allocated once but accessed very often and in a low-latency context. -- Nate
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