Messages in this thread | | | Date | Mon, 28 Apr 2008 14:59:26 +0300 | From | Avi Kivity <> | Subject | Re: stat benchmark |
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Theodore Tso wrote: >> Aside from what has already been proposed there is also the >> readdirplus() route. Unfortunately the people behind this and related >> proposals vanished after the last discussions. I was hoping they >> come back with a revised proposal but perhaps not. Maybe it's time to >> pick up the ball myself. >> >> As a reminder, readdirplus() is an extended readdir() which also >> returns (a subset of) the stat information for the file at the same >> time. The subset part is needed to account for the different >> information contained in the inodes. For most applications the subset >> should be sufficient and therefore all that's needed is a single >> iteration over the directory. >> > > I'm not sure this would help in the cold cache case, which is what > Soeren originally complained about.[1] The problem is whaever > information the user might need won't be store in the directory, so > the filesystem would end having to stat the file anyway, incurring a > disk seek, which was what the user was complaining about. A > readdirplus() would save a whole bunch of system calls if the inode > was already cached, yes, but I'm not sure that's it would be worth the > effort given how small Linux's system call overhead would be. But in > the cold cache case, you end up seeking all over the disk, and the > only thing you can do is to try to keep the inodes close to each > other, and to have either readdir() or the caller of readdir() sort > all of the returned directory entries by inode number to avoid seeking > all over the disk. >
A readdirplus() could sort the inodes according to the filesystem's layout, and additionally issue the stats in parallel, so if you have multiple spindles you get significant additional speedup.
-- error compiling committee.c: too many arguments to function
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