Messages in this thread | | | Subject | Re: [mm/gup] 47e29d32af: phoronix-test-suite.npb.FT.A.total_mop_s -45.0% regression | From | John Hubbard <> | Date | Wed, 18 Nov 2020 11:32:58 -0800 |
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On 11/18/20 10:17 AM, Dan Williams wrote: > On Wed, Nov 18, 2020 at 5:51 AM Jan Kara <jack@suse.cz> wrote: >> >> On Mon 16-11-20 19:35:31, John Hubbard wrote: >>> >>> On 11/16/20 6:48 PM, kernel test robot wrote: >>>> >>>> Greeting, >>>> >>>> FYI, we noticed a -45.0% regression of phoronix-test-suite.npb.FT.A.total_mop_s due to commit: >>>> >>> >>> That's a huge slowdown... >>> >>>> >>>> commit: 47e29d32afba11b13efb51f03154a8cf22fb4360 ("mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages") >>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master >>> >>> ...but that commit happened in April, 2020. Surely if this were a serious >>> issue we would have some other indication...is this worth following up >>> on?? I'm inclined to ignore it, honestly. >> >> Why this was detected so late is a fair question although it doesn't quite >> invalidate the report... > > I don't know what specifically happened in this case, perhaps someone > from the lkp team can comment? However, the myth / contention that > "surely someone else would have noticed by now" is why the lkp project > was launched. Kernels regressed without much complaint and it wasn't > until much later in the process, around the time enterprise distros > rebased to new kernels, did end users start filing performance loss > regression reports. Given -stable kernel releases, 6-7 months is still > faster than many end user upgrade cycles to new kernel baselines. >
I see, thanks for explaining. I'll take a peek, then.
thanks, -- John Hubbard NVIDIA
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