Date: Sun, 20 Oct 2002 16:47:34 -0700 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: Peter Wemm <peter@wemm.org> Cc: Dan Nelson <dnelson@allantgroup.com>, Terry Lambert <tlambert2@mindspring.com>, Brooks Davis <brooks@one-eyed-alien.net>, hackers@FreeBSD.ORG Subject: Re: adding a delay before background fsck Message-ID: <20021020234734.GA390@HAL9000.homeunix.com> In-Reply-To: <20021020201053.1C3092A88D@canning.wemm.org> References: <20021020071930.GA24660@HAL9000.homeunix.com> <20021020201053.1C3092A88D@canning.wemm.org>
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Thus spake Peter Wemm <peter@wemm.org>: > > `Nice' values *do* apply to I/O in -CURRENT. Specifically, if a > > process with a positive nice value attempts to do disk I/O while > > there are other outstanding requests, it is put to sleep for > > p_nice/HZ seconds. I think this feature was added specifically > > for background fsck. If performance is a problem, perhaps it is > > the nice value that needs to be tuned. See Kirk's BSDCon paper on > > snapshots for details. > > Just because something is in a paper that does not mean it is true. > > It is not the case in -current. Read subr_disk.c, and the > #ifdef notquite > around the code. It doesn't work because it assumes that every > 'struct bio' is really embedded in a 'struct buf', which isn't the case. > It used the vnode that was attached to each 'struct buf' to determine > the insert point. 'struct bio' doesn't have associated vnodes. Actually I *did* glance at the code before posting, but I missed the ifdef surrounding the relevant chunk. Oops. Thanks for clarifying! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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