Messages in this thread | | | Date | Fri, 25 Jul 2008 07:54:05 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: Large increase in context switch rate |
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Alex Nixon wrote: > The relevant changeset had caused the blocksize to default to 1024 (as opposed > to 4096) - as a result there was a large increase in the time spent waiting on > pipes. >
Good work!
> Instead of re-adding the line taken out of fs/pipe.c by Theodore I opted instead > to change the default block size for pseudo-filesystems to PAGE_SIZE, to try > avoid making pipe.c inconsistent with Theodore's new approach. > > The performance penalty from these extra context switches is fairly small, but > is magnified when virtualization is involved, hence the desire to keep it lower > if possible. > > > From 4b568a72fc42b52279507eb4d1339e0637ae719a Mon Sep 17 00:00:00 2001 > From: Alex Nixon <t_alexn@alexn-desktop.(none)> > Date: Fri, 25 Jul 2008 11:26:44 +0100 > Subject: [PATCH] VFS: increase pseudo-filesystem block size to PAGE_SIZE. > > Changeset ba52de123d454b57369f291348266d86f4b35070 caused the block size used > by pseudo-filesystems to decrease from PAGE_SIZE to 1024 leading to a doubling > of the number of context switches during a kernbench run. >
Probably worth explicitly noting the effect on pipe buffer size.
> Signed-off-by: Alex Nixon <Alex.Nixon@citrix.com> > --- > fs/libfs.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/libfs.c b/fs/libfs.c > index baeb71e..1add676 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -216,8 +216,8 @@ int get_sb_pseudo(struct file_system_type *fs_type, char *name, > > s->s_flags = MS_NOUSER; > s->s_maxbytes = ~0ULL; > - s->s_blocksize = 1024; > - s->s_blocksize_bits = 10; > + s->s_blocksize = PAGE_SIZE; > + s->s_blocksize_bits = PAGE_SHIFT; > s->s_magic = magic; > s->s_op = ops ? ops : &simple_super_operations; > s->s_time_gran = 1; >
J
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