On 04/18/2013 01:05 AM, zhang.yi20@xxxxxxxxxx wrote: > Darren Hart <dvhart@xxxxxxxxxxxxxxx> 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? > Changes appear to be in the noise, no impact with this load anyway. How many CPUs on your test machine? I presume not 256? -- Darren Hart Intel Open Source Technology Center Yocto Project - Technical Lead - Linux Kernel -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>