To: linux-kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: vfat unlink latency 54.6ms for 128MB files
References: <20050110012330.GA10846@m.safari.iki.fi>
From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Date: Tue, 11 Jan 2005 03:38:32 +0900
In-Reply-To: <20050110012330.GA10846@m.safari.iki.fi> (Sami Farin's message
 of "Mon, 10 Jan 2005 03:23:30 +0200")
Message-ID: <878y71xh7b.fsf@devron.myhome.or.jp>
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Sami Farin <7atbggg02@sneakemail.com> 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...
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

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;
-
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