Dan Williams cfd192c998 libata/ahci: accommodate tag ordered controllers ... commit 8a4aeec8d2 upstream. The AHCI spec allows implementations to issue commands in tag order rather than FIFO order: 5.3.2.12 P:SelectCmd HBA sets pSlotLoc = (pSlotLoc + 1) mod (CAP.NCS + 1) or HBA selects the command to issue that has had the PxCI bit set to '1' longer than any other command pending to be issued. The result is that commands posted sequentially (time-wise) may play out of sequence when issued by hardware. This behavior has likely been hidden by drives that arrange for commands to complete in issue order. However, it appears recent drives (two from different vendors that we have found so far) inflict out-of-order completions as a matter of course. So, we need to take care to maintain ordered submission, otherwise we risk triggering a drive to fall out of sequential-io automation and back to random-io processing, which incurs large latency and degrades throughput. This issue was found in simple benchmarks where QD=2 seq-write performance was 30-50% *greater* than QD=32 seq-write performance. Tagging for -stable and making the change globally since it has a low risk-to-reward ratio. Also, word is that recent versions of an unnamed OS also does it this way now. So, drives in the field are already experienced with this tag ordering scheme. Cc: Dave Jiang <dave.jiang@intel.com> Cc: Ed Ciechanowski <ed.ciechanowski@intel.com> Reviewed-by: Matthew Wilcox <matthew.r.wilcox@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2014-05-13 13:59:43 +02:00
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acpi	ACPI / hotplug: Fix conflicted PCI bridge notify handlers	2013-12-04 10:57:04 -08:00
asm-generic	mm: fix TLB flush race between migration, and change_protection_range	2014-01-09 12:24:23 -08:00
clocksource	clocksource: arch_timer: use virtual counters	2014-01-09 12:24:26 -08:00
crypto	crypto: scatterwalk - Use sg_chain_ptr on chain entries	2013-12-11 22:36:29 -08:00
drm	drm/radeon: 0x9649 is SUMO2 not SUMO	2014-01-09 12:24:22 -08:00
dt-bindings
keys
linux	libata/ahci: accommodate tag ordered controllers	2014-05-13 13:59:43 +02:00
math-emu
media	media: v4l2: added missing mutex.h include to v4l2-ctrls.h	2013-09-26 17:18:26 -07:00
memory
misc
net	tcp: tcp_release_cb() should release socket ownership	2014-04-14 06:42:16 -07:00
pcmcia
ras
rdma
rxrpc
scsi	ore: Fix wrong math in allocation of per device BIO	2014-02-13 13:48:00 -08:00
sound	ALSA: memalloc.h - fix wrong truncation of dma_addr_t	2013-12-20 07:45:06 -08:00
target	iscsi/iser-target: Fix isert_conn->state hung shutdown issues	2014-03-23 21:38:21 -07:00
trace	tracing: Fix array size mismatch in format string	2014-03-31 09:58:12 -07:00
uapi	ALSA: compress: Fix 64bit ABI incompatibility	2013-12-20 07:45:06 -08:00
video	Merge branch 'fbdev-3.10-fixes' of git://gitorious.org/linux-omap-dss2/linux into linux-fbdev/for-3.10-fixes	2013-05-29 17:00:34 +08:00
xen	xenbus: delay xenbus frontend resume if xenstored is not running	2013-05-29 09:04:19 -04:00
Kbuild	UAPI: remove empty Kbuild files	2013-04-30 17:04:09 -07:00