Date: Sun, 23 Sep 2001 13:19:35 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: David Greenman <dg@root.com>, Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp>, bright@wintelcom.net, hackers@FreeBSD.ORG Subject: Re: Conclusions on... was Re: More on the cache_purgeleafdirs() routine Message-ID: <200109232019.f8NKJZL88354@earth.backplane.com> References: <1620.1001272770@critter>
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:Block input operations is the one notable exception and it tells a
:very interesting story: Matts patch results in a 4% increase, but
:combined with vmdirioenable it results in a 21.5% decrease.
:
:That's pretty darn significant: one out of every five I/O have
:been saved.
:
:The reason it has not manifested itself in the "real" number is
:probably the high degree of parallelism in the task which practically
:ensures that the CPU will not go idle.
:
:I suggest we let Matt's patch depend on the vmiodirenable sysctl
:and change the default for that.
:
:If there are no bad side effects found in the next couple of months,
:then kill the sysctl and lets be done with it.
:
:Poul-Henning
Very interesting! I agree completely. I will instrument the code
to make the namei cache check conditional on vmiodirenable. I will
also add a sysctl to change the check condition to test for leaf
directories or not (closer to what Seigo's code accomplished) so we can
test for differences there. If we can get that 4% down the code will
be more acceptable.
The results make a lot of sense, especially if the machine has sufficient
memory to cache most of the source tree. Increasing the number of
vnode reclaims will increase I/O on directories, especially for something
like a buildworld which is doing major path expansions up the wazoo.
Turning on vmiodirenable in a buildworld situation will decrease I/O
significantly.
-Matt
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