Date: Sun, 19 Dec 1999 11:29:46 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Peter Wemm <peter@netplex.com.au> Cc: Greg Lehey <grog@lemis.com>, FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Subject: Re: Recent current hangs frequently for 1 to 2 seconds. Message-ID: <199912191929.LAA06659@apollo.backplane.com> References: <19991219091857.914021CA0@overcee.netplex.com.au>
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:> driver, but it's also possible that they are due to a bug in the
:> buffer cache flushing code which the following patch fixes. So try
:> the patch and see if that fixes your problem. If it doesn't then
:> we can at least rule it out as being the cause of the problem you
:> are seeing.
:[..]
:
:Just one comment.. You've replaced vfs_bio's call to speedup_syncer() with
:a bufdaemon speedup.. Granted I don't understand the details here, but
:I'm curious why? (or why not use both?) The reason I ask is that I wonder
:whether removing of the speedup of the vnode cleanup rate is a good idea or
:not.. or if the bufdaemon speedup does this as a side effect via the hooks
:softupdates has got in the bio system. This is not a criticism, just a
:request for enlightenment. :-)
speedup_syncer() was designed for softupdates to allow softupdates to
regulate the number of pending transactions. The problem with it,
though, is that calling the function results in a 'slow reaction' by
the system rather then an 'immediate reaction', and in this particular
case we need an immediate reaction. A slow reaction gets us nowhere
(gets us multi-second delays, in fact).
bd_speedup() wakes up the buf_daemon and as part of the patch the
buf_daemon has been redesigned to handle the 'immediate reaction' case
without compromising its dynamic stability characteristics (which are
what tend to make it efficient under normal operation).
-Matt
Matthew Dillon
<dillon@backplane.com>
:
:> @@ -1571,9 +1573,8 @@
:> flags = VFS_BIO_NEED_ANY;
:> }
:>
:> - /* XXX */
:> + bd_speedup(); /* heeeelp */
:>
:> - (void) speedup_syncer();
:> needsbuffer |= flags;
:> while (needsbuffer & flags) {
:> if (tsleep(&needsbuffer, (PRIBIO + 4) | slpflag,
:
:Cheers,
:-Peter
:
:
:
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