On 04/06/2012 11:43 PM, Dan Williams wrote: > [adding Boaz since he also made an attempt at fixing this] > > http://marc.info/?l=linux-crypto-vger&m=131829241111450&w=2 > > ...I had meant to follow up on this, but was buried in 'isci' issues. > > Sorry was traveling. Yes I have an old fix for this. Which I need to cleanup and retest. My original problem was an hang in UML, but I noticed the timing problems as well. Please give me til the end of the week to settle in and come up to speed. [Current patch: http://marc.info/?l=linux-crypto-vger&m=131829242311458&w=2] Thanks Boaz > On Tue, Apr 3, 2012 at 4:56 PM, Jim Kukunas > <james.t.kukunas@xxxxxxxxxxxxxxx> wrote: >> On Tue, Apr 03, 2012 at 11:23:16AM +0100, John Robinson wrote: >>> On 02/04/2012 23:48, Jim Kukunas wrote: >>>> On Sat, Mar 31, 2012 at 12:38:56PM +0100, John Robinson wrote: >>> [...] >>>>> I just noticed in my logs the other day (recent el5 kernel on a Core 2): >>>>> >>>>> raid5: automatically using best checksumming function: generic_sse >>>>> generic_sse: 7805.000 MB/sec >>>>> raid5: using function: generic_sse (7805.000 MB/sec) >>> [...] >>>>> raid6: using algorithm sse2x4 (8237 MB/s) >>>>> >>>>> I was just wondering how it's possible to do the RAID6 Q calculation >>>>> faster than the RAID5 XOR calculation - or am I reading this log excerpt >>>>> wrongly? >>>> >>>> Out of curiosity, are you running with CONFIG_PREEMPT=y? >>> >>> No. Here's an excerpt from my .config: >>> >>> # CONFIG_PREEMPT_NONE is not set >>> CONFIG_PREEMPT_VOLUNTARY=y >>> # CONFIG_PREEMPT is not set >>> CONFIG_PREEMPT_BKL=y >>> CONFIG_PREEMPT_NOTIFIERS=y >>> >>> But this is a Xen dom0 kernel, 2.6.18-308.1.1.el5.centos.plusxen. Now, a >>> non-Xen kernel (2.6.18-308.1.1.el5) says: >>> raid5: automatically using best checksumming function: generic_sse >>> generic_sse: 11892.000 MB/sec >>> raid5: using function: generic_sse (11892.000 MB/sec) >>> raid6: int64x1 2644 MB/s >>> raid6: int64x2 3238 MB/s >>> raid6: int64x4 3011 MB/s >>> raid6: int64x8 2503 MB/s >>> raid6: sse2x1 5375 MB/s >>> raid6: sse2x2 5851 MB/s >>> raid6: sse2x4 9136 MB/s >>> raid6: using algorithm sse2x4 (9136 MB/s) >>> >>> Looks like it loses a chunk of performance running as a Xen dom0. >>> >>> Even still, 11892 MB/s for XOR vs 9136 MB/s for XOR+Q - it still seems >>> remarkable that the XOR can't be done several times faster than the Q. >> >> Taking a look at do_xor_speed, I see two issues which might be the cause >> of the disparity you reported. >> >> 0) In the RAID5 xor benchmark, we get the current jiffy, then run do_2() until >> the jiffy increments. This means we could potentially be testing for less >> than a full jiffy. The RAID6 benchmark handles this by obtaining the current >> jiffy, then calling cpu_relax() until the jiffy increments, and then running >> the test. This is addressed by my first patch. >> >> 1) The only way I could reproduce your findings of a higher throughput for >> RAID6 than for RAID5 xor checksumming was with CONFIG_PREEMPT=y. It seems >> that you encountered this while running as XEN dom0. Currently, we disable >> preemption during the RAID6 benchmark, but don't in the RAID5 benchmark. >> This is addressed by my second patch. >> >> I've added linux-crypto to the discussion as both of these patches affect >> code in crypto/ >> >> Thanks. >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
