Date: Thu, 21 Jun 2012 22:36:04 -0400 From: Charles Owens <cowens@greatbaysoftware.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-stable@freebsd.org Subject: Re: mfi(4) IO performance regression, post 8.1 Message-ID: <4FE3DA14.9090506@greatbaysoftware.com> In-Reply-To: <201206150804.46341.jhb@freebsd.org> References: <4FDABA0B.5030702@greatbaysoftware.com> <201206150804.46341.jhb@freebsd.org>
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On 6/15/12 8:04 AM, John Baldwin wrote:
> On Friday, June 15, 2012 12:28:59 am Charles Owens wrote:
>> Hello FreeBSD folk,
>>
>> We're seeing what appears to be a storage performance regression as we
>> try to move from 8.1 (i386) to 8.3. We looked at 8.2 also and it
>> appears that the regression happened between 8.1 and 8.2.
>>
>> Our system is an Intel S5520UR Server with 12 GB RAM, dual 4-core CPUs.
>> Storage is a LSI MegaSAS 1078 controller (mfi) in a RAID-10
>> configuration, using UFS + geom_journal for filesystem.
>>
>> Postgresql performance, as seen via pgbench, dropped by approx 20%.
>> This testing was done with our usual PAE-enabled kernels. We then went
>> back to GENERIC kernels and did comparisons using "bonnie", results
>> below. Following that is a kernel boot log.
>>
>> Notably, we're seeing this regression only with our RAID mfi(4) based
>> systems. Notably, from looking at FreeBSD source changelogs it appears
>> that the mfi(4) code has seen some changes since 8.1.
> Between 8.1 and 8.2 mfi has not had any significant changes. The only changes
> made to sys/dev/mfi were to add a new constant:
>
>> svn diff svn+ssh://svn.freebsd.org/base/releng/8.1/sys/dev/mfi
> svn+ssh://svn.freebsd.org/base/releng/8.2/sys/dev/mfi
> Index: mfireg.h
> ===================================================================
> --- mfireg.h (.../8.1/sys/dev/mfi) (revision 237134)
> +++ mfireg.h (.../8.2/sys/dev/mfi) (revision 237134)
> @@ -975,7 +975,9 @@
> MFI_PD_STATE_OFFLINE = 0x10,
> MFI_PD_STATE_FAILED = 0x11,
> MFI_PD_STATE_REBUILD = 0x14,
> - MFI_PD_STATE_ONLINE = 0x18
> + MFI_PD_STATE_ONLINE = 0x18,
> + MFI_PD_STATE_COPYBACK = 0x20,
> + MFI_PD_STATE_SYSTEM = 0x40
> };
>
> union mfi_ld_ref {
>
> The difference in write performance must be due to something else. You
> mentioned you are using UFS + gjournal. I think gjournal uses BIO_FLUSH, so I
> wonder if this is related:
>
> ------------------------------------------------------------------------
> r212939 | gibbs | 2010-09-20 19:39:00 -0400 (Mon, 20 Sep 2010) | 61 lines
>
> MFC 212160:
>
> Correct bioq_disksort so that bioq_insert_tail() offers barrier semantic.
> Add the BIO_ORDERED flag for struct bio and update bio clients to use it.
>
> The barrier semantics of bioq_insert_tail() were broken in two ways:
>
> o In bioq_disksort(), an added bio could be inserted at the head of
> the queue, even when a barrier was present, if the sort key for
> the new entry was less than that of the last queued barrier bio.
>
> o The last_offset used to generate the sort key for newly queued bios
> did not stay at the position of the barrier until either the
> barrier was de-queued, or a new barrier (which updates last_offset)
> was queued. When a barrier is in effect, we know that the disk
> will pass through the barrier position just before the
> "blocked bios" are released, so using the barrier's offset for
> last_offset is the optimal choice.
>
> sys/geom/sched/subr_disk.c:
> sys/kern/subr_disk.c:
> o Update last_offset in bioq_insert_tail().
>
> o Only update last_offset in bioq_remove() if the removed bio is
> at the head of the queue (typically due to a call via
> bioq_takefirst()) and no barrier is active.
>
> o In bioq_disksort(), if we have a barrier (insert_point is non-NULL),
> set prev to the barrier and cur to it's next element. Now that
> last_offset is kept at the barrier position, this change isn't
> strictly necessary, but since we have to take a decision branch
> anyway, it does avoid one, no-op, loop iteration in the while
> loop that immediately follows.
>
> o In bioq_disksort(), bypass the normal sort for bios with the
> BIO_ORDERED attribute and instead insert them into the queue
> with bioq_insert_tail(). bioq_insert_tail() not only gives
> the desired command order during insertion, but also provides
> barrier semantics so that commands disksorted in the future
> cannot pass the just enqueued transaction.
>
> sys/sys/bio.h:
> Add BIO_ORDERED as bit 4 of the bio_flags field in struct bio.
>
> sys/cam/ata/ata_da.c:
> sys/cam/scsi/scsi_da.c
> Use an ordered command for SCSI/ATA-NCQ commands issued in
> response to bios with the BIO_ORDERED flag set.
>
> sys/cam/scsi/scsi_da.c
> Use an ordered tag when issuing a synchronize cache command.
>
> Wrap some lines to 80 columns.
>
> sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
> sys/geom/geom_io.c
> Mark bios with the BIO_FLUSH command as BIO_ORDERED.
>
> Sponsored by: Spectra Logic Corporation
> ------------------------------------------------------------------------
>
> Can you try perhaps commenting out the 'bp->bio_flags |= BIO_ORDERED' line
> changed in geom_io.c in 8.2? That would be effectively reverting this
> portion of the diff:
>
> Index: geom_io.c
> ===================================================================
> --- geom_io.c (.../8.1/sys/geom) (revision 237134)
> +++ geom_io.c (.../8.2/sys/geom) (revision 237134)
> @@ -265,6 +265,7 @@
> g_trace(G_T_BIO, "bio_flush(%s)", cp->provider->name);
> bp = g_alloc_bio();
> bp->bio_cmd = BIO_FLUSH;
> + bp->bio_flags |= BIO_ORDERED;
> bp->bio_done = NULL;
> bp->bio_attribute = NULL;
> bp->bio_offset = cp->provider->mediasize;
>
John... thanks for the suggestion. I've built and tested a kernel with
this change made. Result: no change (same performance as with
8.2-GENERIC). Any thoughts as to where to go next?
Thank you,
Charles
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