Messages in this thread | | | Subject | Re: Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage | From | zhang.yi20@zte ... | Date | Thu, 18 Apr 2013 16:05:19 +0800 |
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Darren Hart <dvhart@linux.intel.com> wrote on 2013/04/17 23:51:36:
> On 04/17/2013 08:26 AM, Dave Hansen wrote: > > On 04/17/2013 07:18 AM, Darren Hart wrote: > >>>> This also needs a comment in futex.h describing the usage of the > >>>> offset field in union futex_key as well as above get_futex_key > >>>> describing the key for shared mappings. > >>>> > >>> As far as I know , the max size of one hugepage is 1 GBytes for > >>> x86 cpu. Can some other cpus support greater hugepage even more > >>> than 4 GBytes? If so, we can change the type of 'offset' from int > >>> to long to avoid truncating. > >> > >> I discussed this with Dave Hansen, on CC, and he thought we needed > >> 9 bits, so even on x86 32b we should be covered. > > > > I think the problem is actually on 64-bit since you still only have > > 32-bits in an 'int' there. > > > > I guess it's remotely possible that we could have some > > mega-super-huge-gigantic pages show up in hardware some day, or that > > somebody would come up with software-only one. I bet there's a lot > > more code that will break in the kernel than this futex code, though. > > > > The other option would be to start #defining some build-time constant > > for what the largest possible huge page size is, then BUILD_BUG_ON() > > it. > > > > Or you can just make it a long ;) > > If we make it a long I'd want to see futextest performance tests before > and after. Messing with the futex_key has been known to have bad results > in the past :-) > > --
I have run futextest/performance/futex_wait for testing, 5 times before make it long: futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10215 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 9862 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10081 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10060 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10081 Kiter/s
And 5 times after make it long: futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 9940 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10204 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 9901 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10152 Kiter/s
futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10060 Kiter/s
Seems OK, is it?
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