Date: Thu, 27 Jan 2005 00:40:08 +0000 (GMT) From: Robert Watson <rwatson@freebsd.org> To: Mike Tancsa <mike@sentex.net> Cc: freebsd-questions@freebsd.org Subject: Re: FreeBSD 5.3 I/O Performance / Linux 2.6.10 | Continued Discussion Message-ID: <Pine.NEB.3.96L.1050127003735.26815Z-100000@fledge.watson.org> In-Reply-To: <Pine.NEB.3.96L.1050127002905.26815X-100000@fledge.watson.org>
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On Thu, 27 Jan 2005, Robert Watson wrote: > While it's not for the feint of heart, it might be interesting to see > how results compare in 6-CURRENT + debugging of various sorts (including > malloc) turned off, and debug.mpsafevfs turned on. One possible issue > with the twe/twa drivers is that they are currently MPSAFE, so may see > substantial contention (and hence additional latency). The move to an > MPSAFE VFS will help with that a lot, I should think. And, if you're in the mood for hacking code, and promise not to use snapshots, try making vfs_subr.c:vn_start_write(), vfs_subr.c:vn_write_suspend_wait(), vfs_subr.c:vn_finished_write(), vfs_subr.c:vfs_write_suspend(), and vfs_subr.c:vfs_write_resume() into noop's. These calls are used to avoid some deadlock scenarios associated with snapshot generation, but they also introduce a small but non-trivial amount of overhead to a number of operations. Since you're set up to do some testing, knowing how much of that cost is from these operations should be quite interesting. Robert N M Watson
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