The reason rfs3_{write|create} waiting longer in txg_wait_open is because
there is a syncing txg taking longer to complete.
You may want to trace and track the syncing txg to get the reason for the
delay.
--
Prabahar.
On Sun, Nov 23, 2008 at 05:51:44PM -0800, Amer Ather wrote:
> IHAC who is seeing very slow NFS transactions over ZFS. rfs3_write(),
> rfs3_create() and others are taking in the order of 17-20 seconds to
> complete. Profiling these transactions showing most of the time is spent
> in txg_wait_open() - waiting for transaction group to open.
>
> We tried "zfs_nocacheflush: but it did n't help. iostat showing good
> service time (<10ms).
>
> System is running Solaris 10 - 137137-09
>
> 00000301b616ec00 3000813e168 3017b9e3798 2 59 6002296f966
> PC: cv_wait+0x38 CMD:
> mv camshot_081118_000029.jpg camshot_081118_000059.jpg
> camshot_081118_000129.j
> p
> stack pointer for thread 301b616ec00: 2a104a9ceb1
> [ 000002a104a9ceb1 cv_wait+0x38() ]
> txg_wait_open+0x54()
> zfs_write+0x34c()
> fop_write+0x20()
> write+0x268()
> syscall_trap32+0xcc()
>
> Timing txg_wait_open() shows:
>
> txg_wait_open delay
> DELAY
> value ------------- Distribution ------------- count
> 4294967296 | 0
> 8589934592 |@ 1
> 17179869184 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 33
> 34359738368 | 0
>
> txg_wait_open delay
> DELAY
> value ------------- Distribution ------------- count
> 134217728 | 0
> 268435456 |@@ 2
> 536870912 | 0
> 1073741824 | 0
> 2147483648 |@ 1
> 4294967296 | 0
> 8589934592 |@@@@@@@ 7
> 17179869184 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 29
> 34359738368 | 0
>
> DTrace script:
> #!/usr/sbin/dtrace -qs
> fbt::txg_wait_open:entry
> {
> self->t = timestamp;
> }
> fbt::txg_wait_open:return
> /self->t/
> {
> @a["DELAY"] = quantize(timestamp - self->t);
> }
> tick-5sec {
> printf("\ntxg_wait_open delay");
> printa(@a);
> trunc(@a);
> }
>
>
> I have also profiled rfs3_write(), rfs3_create() and other using DTrace
> and taken time delta and stack at each frame on all functions called by
> rfs3_* and see txg_wait_open() is the one taking majority of the time.
>
> Thanks,
> Amer.
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss@opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
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