Re: vfat unlink latency 54.6ms for 128MB files

[Robert Hardy]

On Tue, 11 Jan 2005, OGAWA Hirofumi wrote:
> Sami Farin <7atbggg02@xxxxxxxxxxxxxx> writes:
>
> > Just wondering, when I remove a 128MB file on vfat partition
> > (usb-storage, memcard reader), it causes 54.6ms latency
> > in rtc_latencytest...  latency seems to increase linearly
> > as the filesize grows.  I calculated 1s would be reached with
> > 2344MB file but I didn't bother trying that yet.
> > Are there any possible fixes for fat fs so
> > that it doesn't disable interrupts for that long a time?
>
> The fatfs itself doesn't disable any interrupt.  I guess the thing
> depending on file size is the fat_free().
>
> So, the following patch may change the behavior...

diff -up linux-2.6.10/fs/fat/cache.c.orig linux-2.6.10/fs/fat/cache.c
--- linux-2.6.10/fs/fat/cache.c.orig    2004-12-25 06:35:24.000000000 +0900
+++ linux-2.6.10/fs/fat/cache.c 2005-01-11 03:34:54.000000000 +0900
@@ -491,6 +491,8 @@ int fat_free(struct inode *inode, int sk
                if (MSDOS_SB(sb)->free_clusters != -1)
                        MSDOS_SB(sb)->free_clusters++;
                inode->i_blocks -= MSDOS_SB(sb)->cluster_size >> 9;
+
+               cond_resched();
        } while (nr != FAT_ENT_EOF);
        fat_clusters_flush(sb);
        nr = 0;
-

Thanks for your patchset.tar (in another thread) from:
Thu, 30 Dec 2004 12:02:14 +0900.

Based on the patch above, is an additional cond_resched() call required
somewhere in your 2004/12/30 patchset?

In your 2004/12/30 patchset, if I am reading it correctly, fat_free seems to
have moved from cache.c to file.c and the code isn't similar enough for me
to see where a cond_resched() could be added.

Perhaps you have already have a newer patchset?

Thanks for your time.

Regards,
Rob

--
---------------------"Happiness is understanding."----------------------
Robert Hardy, B.Eng Computer Systems                  C.E.O. Webcon Inc.
rhardy <at> webcon <dot> ca    GPG Key available          (613) 276-7327
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