On 05/23/2010 06:31 PM, Michael S. Tsirkin wrote: > On Thu, May 20, 2010 at 02:38:16PM +0930, Rusty Russell wrote: > >> On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote: >> >>> On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote: >>> >>>>> Note that this is a exclusive->shared->exclusive bounce only, too. >>>>> >>>>> >>>> A bounce is a bounce. >>>> >>> I tried to measure this to show that you were wrong, but I was only able >>> to show that you're right. How annoying. Test code below. >>> >> This time for sure! >> > > What do you see? > On my laptop: > [mst@tuck testring]$ ./rusty1 share 0 1 > CPU 1: share cacheline: 2820410 usec > CPU 0: share cacheline: 2823441 usec > [mst@tuck testring]$ ./rusty1 unshare 0 1 > CPU 0: unshare cacheline: 2783014 usec > CPU 1: unshare cacheline: 2782951 usec > [mst@tuck testring]$ ./rusty1 lockshare 0 1 > CPU 1: lockshare cacheline: 1888495 usec > CPU 0: lockshare cacheline: 1888544 usec > [mst@tuck testring]$ ./rusty1 lockunshare 0 1 > CPU 0: lockunshare cacheline: 1889854 usec > CPU 1: lockunshare cacheline: 1889804 usec > Ugh, can the timing be normalized per operation? This is unreadable. > So locked version seems to be faster than unlocked, > and share/unshare not to matter? > May be due to the processor using the LOCK operation as a hint to reserve the cacheline for a bit. > same on a workstation: > [root@qus19 ~]# ./rusty1 unshare 0 1 > CPU 0: unshare cacheline: 6037002 usec > CPU 1: unshare cacheline: 6036977 usec > [root@qus19 ~]# ./rusty1 lockunshare 0 1 > CPU 1: lockunshare cacheline: 5734362 usec > CPU 0: lockunshare cacheline: 5734389 usec > [root@qus19 ~]# ./rusty1 lockshare 0 1 > CPU 1: lockshare cacheline: 5733537 usec > CPU 0: lockshare cacheline: 5733564 usec > > using another pair of CPUs gives a more drastic > results: > > [root@qus19 ~]# ./rusty1 lockshare 0 2 > CPU 2: lockshare cacheline: 4226990 usec > CPU 0: lockshare cacheline: 4227038 usec > [root@qus19 ~]# ./rusty1 lockunshare 0 2 > CPU 0: lockunshare cacheline: 4226707 usec > CPU 2: lockunshare cacheline: 4226662 usec > [root@qus19 ~]# ./rusty1 unshare 0 2 > CPU 0: unshare cacheline: 14815048 usec > CPU 2: unshare cacheline: 14815006 usec > > That's expected. Hyperthread will be fastest (shared L1), shared L2/L3 will be slower, cross-socket will suck. -- error compiling committee.c: too many arguments to function _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
