i386/68719: [usb] USB 2.0 mobil rack+ fat32 performance problem
Bruce Evans
bde at zeta.org.au
Mon May 30 03:50:05 PDT 2005
The following reply was made to PR i386/68719; it has been noted by GNATS.
From: "Bruce Evans" <bde at zeta.org.au>
To: <james>
Cc: <freebsd-fs at freebsd.org>,
<freebsd-gnats-submit at freebsd.org>,
<banhalmi at field.hu>
Subject: Re: i386/68719: [usb] USB 2.0 mobil rack+ fat32 performance problem
Date: Mon, 30 May 2005 11:46:06 +0100
On Mon, 30 May 2005, Bruce Evans wrote:
> On Sun, 29 May 2005, Dominic Marks wrote:
>> I have been experimenting in msdosfs_read and I have managed to come up
>> with
>> something that works, but I'm sure it is flawed. On large file reads it
>> will
>> ...
>> %%
>> Index: msdosfs_vnops.c
>> ===================================================================
>> RCS file: /usr/cvs/src/sys/fs/msdosfs/msdosfs_vnops.c,v
>> retrieving revision 1.149.2.1
>> diff -u -r1.149.2.1 msdosfs_vnops.c
>> --- msdosfs_vnops.c 31 Jan 2005 23:25:56 -0000 1.149.2.1
>> +++ msdosfs_vnops.c 29 May 2005 14:10:18 -0000
>> @@ -565,14 +567,21 @@
>> error = bread(pmp->pm_devvp, lbn, blsize, NOCRED,
>> &bp);
>> } else {
>> blsize = pmp->pm_bpcluster;
>> - rablock = lbn + 1;
>> - if (seqcount > 1 &&
>> - de_cn2off(pmp, rablock) < dep->de_FileSize) {
>> - rasize = pmp->pm_bpcluster;
>> - error = breadn(vp, lbn, blsize,
>> - &rablock, &rasize, 1, NOCRED, &bp);
>> + /* XXX what is the best value for crsize? */
>> + crsize = blsize * nblks > MAXBSIZE ? MAXBSIZE :
>> blsize * nblks;
>> + if ((vp->v_mount->mnt_flag & MNT_NOCLUSTERR) == 0) {
>> + error = cluster_read(vp, dep->de_FileSize,
>> lbn,
>> + crsize, NOCRED, uio->uio_resid,
>> seqcount, &bp);
>
> crsize should be just the block size (cluster size in msdosfs and
> blsize variable here) according to this code in all other file systems.
> ...
The main problem is that VOP_BMAP() is not fully implemented for msdosfs.
msdosfs_bmap() only has a stub which pretends that clustering ins never
possible:
% /*
% * vp - address of vnode file the file
% * bn - which cluster we are interested in mapping to a filesystem block number.
% * vpp - returns the vnode for the block special file holding the filesystem
% * containing the file of interest
% * bnp - address of where to return the filesystem relative block number
% */
This comment rotted in 1994 when 4.4BSD packed the args into a struct
and added the a_runp and a_runb args to support clustering.
% static int
% msdosfs_bmap(ap)
% struct vop_bmap_args /* {
% struct vnode *a_vp;
% daddr_t a_bn;
% struct vnode **a_vpp;
% daddr_t *a_bnp;
% int *a_runp;
% int *a_runb;
% } */ *ap;
% {
% struct denode *dep = VTODE(ap->a_vp);
% daddr_t blkno;
% int error;
%
% if (ap->a_vpp != NULL)
% *ap->a_vpp = dep->de_devvp;
% if (ap->a_bnp == NULL)
% return (0);
% if (ap->a_runp) {
% /*
% * Sequential clusters should be counted here.
^^^^^^^^^
% */
% *ap->a_runp = 0;
% }
% if (ap->a_runb) {
% *ap->a_runb = 0;
% }
% error = pcbmap(dep, ap->a_bn, &blkno, 0, 0);
% *ap->a_bnp = blkno;
% return (error);
% }
Here is a cleaned up version of the patch to add (not actually working)
clustering to msdosfs_read().
%%%
Index: msdosfs_vnops.c
===================================================================
RCS file: /home/ncvs/src/sys/fs/msdosfs/msdosfs_vnops.c,v
retrieving revision 1.147
diff -u -2 -r1.147 msdosfs_vnops.c
--- msdosfs_vnops.c 4 Feb 2004 21:52:53 -0000 1.147
+++ msdosfs_vnops.c 30 May 2005 08:57:02 -0000
@@ -541,5 +555,7 @@
if (uio->uio_offset >= dep->de_FileSize)
break;
+ blsize = pmp->pm_bpcluster;
lbn = de_cluster(pmp, uio->uio_offset);
+ rablock = lbn + 1;
/*
* If we are operating on a directory file then be sure to
@@ -556,15 +573,15 @@
break;
error = bread(pmp->pm_devvp, lbn, blsize, NOCRED, &bp);
+ } else if (de_cn2off(pmp, rablock) >= dep->de_FileSize) {
+ error = bread(vp, lbn, blsize, NOCRED, &bp);
+ } else if ((vp->v_mount->mnt_flag & MNT_NOCLUSTERR) == 0) {
+ error = cluster_read(vp, dep->de_FileSize, lbn, blsize,
+ NOCRED, uio->uio_resid, seqcount, &bp);
+ } else if (seqcount > 1) {
+ rasize = blsize;
+ error = breadn(vp, lbn,
+ blsize, &rablock, &rasize, 1, NOCRED, &bp);
} else {
- blsize = pmp->pm_bpcluster;
- rablock = lbn + 1;
- if (seqcount > 1 &&
- de_cn2off(pmp, rablock) < dep->de_FileSize) {
- rasize = pmp->pm_bpcluster;
- error = breadn(vp, lbn, blsize,
- &rablock, &rasize, 1, NOCRED, &bp);
- } else {
- error = bread(vp, lbn, blsize, NOCRED, &bp);
- }
+ error = bread(vp, lbn, blsize, NOCRED, &bp);
}
if (error) {
%%%
I rearranged the code to be almost lexically identical with that in
ffs_read().
I only tested this on a relatively fast ATA drive. It made little
difference. Most writes were clustered to give a block size of 64K
and write speed of over 40+MB/s until the disk is nearly full, but
reads weren't clustered with or without the patch so the block size
remained at the fs block size (4K); the drive handles this block size
mediocrely and gave a read speed of 20+MB/sec. (The drive is a WDC
1200JB-00CRA1. This drive has the interesting behaviour of giving
almost the same mediocre read speed for all block sizes between 2.5K
and 19.5K. A block size 20K gives maximal speed which is about twice
as fast as the speed for a block size of 19.5K.)
Both reading and writing a 1GB file to/from msdosfs caused noticable
buffer resource problems. Accesses to other file systems on the same
disk sometimes blocked for many seconds. I have debugging code in
getblk(). It reported that a process waited 17 seconds in or near
getblk(). The process only stopped waiting because I suspended the
process accessing msdosfs. This may be a local bug.
Bruce
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