On Mon, Mar 02, 2015 at 11:47:52AM -0800, Linus Torvalds wrote: > On Sun, Mar 1, 2015 at 5:04 PM, Dave Chinner <[email protected]> wrote: > > > > Across the board the 4.0-rc1 numbers are much slower, and the > > degradation is far worse when using the large memory footprint > > configs. Perf points straight at the cause - this is from 4.0-rc1 > > on the "-o bhash=101073" config: > > > > - 56.07% 56.07% [kernel] [k] > > default_send_IPI_mask_sequence_phys > > - 99.99% physflat_send_IPI_mask > > - 99.37% native_send_call_func_ipi > .. > > > > And the same profile output from 3.19 shows: > > > > - 9.61% 9.61% [kernel] [k] > > default_send_IPI_mask_sequence_phys > > - 99.98% physflat_send_IPI_mask > > - 96.26% native_send_call_func_ipi > ... > > > > So either there's been a massive increase in the number of IPIs > > being sent, or the cost per IPI have greatly increased. Either way, > > the result is a pretty significant performance degradatation. .... > I assume it's the mm queue from Andrew, so adding him to the cc. There > are changes to the page migration etc, which could explain it. > > There are also a fair amount of APIC changes in 4.0-rc1, so I guess it > really could be just that the IPI sending itself has gotten much > slower. Adding Ingo for that, although I don't think > default_send_IPI_mask_sequence_phys() itself hasn't actually changed, > only other things around the apic. So I'd be inclined to blame the mm > changes. > > Obviously bisection would find it..
Yes, though the time it takes to do a 13 step bisection means it's something I don't do just for an initial bug report. ;) Anyway, the difference between good and bad is pretty clear, so I'm pretty confident the bisect is solid: 4d9424669946532be754a6e116618dcb58430cb4 is the first bad commit commit 4d9424669946532be754a6e116618dcb58430cb4 Author: Mel Gorman <[email protected]> Date: Thu Feb 12 14:58:28 2015 -0800 mm: convert p[te|md]_mknonnuma and remaining page table manipulations With PROT_NONE, the traditional page table manipulation functions are sufficient. [[email protected]: fix compiler warning in pmdp_invalidate()] [[email protected]: fix build with STRICT_MM_TYPECHECKS] Signed-off-by: Mel Gorman <[email protected]> Acked-by: Linus Torvalds <[email protected]> Acked-by: Aneesh Kumar <[email protected]> Tested-by: Sasha Levin <[email protected]> Cc: Benjamin Herrenschmidt <[email protected]> Cc: Dave Jones <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Kirill Shutemov <[email protected]> Cc: Paul Mackerras <[email protected]> Cc: Rik van Riel <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> :040000 040000 50985a3f84e80bb2bdd049d4f34739d99436f988 1bc79bfac2c138844373b603f9bc5914f0d010f3 M arch :040000 040000 ea69bcd1c59f832a4b012a57b4eb1d0c7516947d 0822692fa6c356952e723b56038585716fa51723 M include :040000 040000 c11960b9f1ee72edb08dc3fdc46f590fb1d545f7 f5d17ff5b639adcb7363a196a9efe70f2a7312b5 M mm Cheers, Dave. -- Dave Chinner [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
