diff options
author | Grant Grundler <grundler@google.com> | 2010-04-14 21:43:32 -0400 |
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committer | Jeff Garzik <jgarzik@redhat.com> | 2010-05-14 17:08:02 -0400 |
commit | 4f2c774856708bccecb74c0e6296e9e2c9136ee1 (patch) | |
tree | 33ebceafd0f2f21b155dde40344addf45e2cb4ed /drivers/ata/pata_hpt37x.c | |
parent | fbaf666b854c04b2d8ebca17114ee409ddea08b5 (diff) |
[libata] Disable R_OK (Early ACK) on SII 3726 PMP
In 2009, While running "cache read" performance test of drives behind
SII PMP we encountered a "all 5 drives" timeout on more than 30% of the
machines under test. This patch reduces the rate by a factor of about 70.
Low enough that we didn't care to further investigate the issue.
Performance impact with any sort of "normal" use was ~2%+ CPU and less
than 1% throughput degradation. Worst case impact (cached read) was
6% IOPS reduction. This is with NCQ off (q=1) but I believe FIS based
switching enabled in the SATA driver.
The patch disables "Early ACK" in the 3726 port multiplier.
"Early ACK" is issued when device sends a FIS to the host (via PMP)
and the PMP sends an ACK immediately back to the device - well before
the host gets the response. Under worst case IOPs load (cached read
test) and more than 2 PMPs connected to a 4-port SATA controller,
I suspect the time to service all of the PMPs is exceeding the PMPs
ability to keep track of outstanding FIS it owes the Host. Reducing
the number of PMPs to 2 (or 1) reduces the frequency by several orders
of magnitude. Kudos to Gwendal for initial debugging of this issue.
[Any errors in the description are mine, not his.]
Patch is currently in production on Google servers.
Signed-off-by: Grant Grundler <grundler@google.com>
Signed-off-by: Gwendal Grignou <gwendal@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Diffstat (limited to 'drivers/ata/pata_hpt37x.c')
0 files changed, 0 insertions, 0 deletions