On Sun, May 23, 2010 at 07:03:10PM +0300, Avi Kivity wrote: > On 05/23/2010 06:51 PM, Michael S. Tsirkin wrote: >>> >>>> 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. >>> >> Maybe we should use atomics on index then? >> > > This should only be helpful if you access the cacheline several times in > a row. That's not the case in virtio (or here). > > I think the problem is that LOCKSHARE and SHARE are not symmetric, so > they can't be directly compared. > >> OK, after adding mb in code patch will be sent separately, >> the test works for my workstation. locked is still fastest, >> unshared sometimes shows wins and sometimes loses over shared. >> >> [root@qus19 ~]# ./cachebounce share 0 1 >> CPU 0: share cacheline: 6638521 usec >> CPU 1: share cacheline: 6638478 usec >> > > 66 ns? nice. > >> [root@qus19 ~]# ./cachebounce share 0 2 >> CPU 0: share cacheline: 14529198 usec >> CPU 2: share cacheline: 14529156 usec >> > > 140 ns, not too bad. I hope I'm not misinterpreting the results. > > -- > error compiling committee.c: too many arguments to function Here's another box: here the fastest option is shared, slowest unshared, lock is in the middle. [root@virtlab16 testring]# sh run 0 2 CPU 2: share cacheline: 3304728 usec CPU 0: share cacheline: 3304784 usec CPU 0: unshare cacheline: 6283248 usec CPU 2: unshare cacheline: 6283224 usec CPU 2: lockshare cacheline: 4018567 usec CPU 0: lockshare cacheline: 4018609 usec CPU 2: lockunshare cacheline: 4041791 usec CPU 0: lockunshare cacheline: 4041832 usec [root@virtlab16 testring]# [root@virtlab16 testring]# [root@virtlab16 testring]# [root@virtlab16 testring]# sh run 0 1 CPU 1: share cacheline: 8306326 usec CPU 0: share cacheline: 8306324 usec CPU 0: unshare cacheline: 19571697 usec CPU 1: unshare cacheline: 19571578 usec CPU 0: lockshare cacheline: 11281566 usec CPU 1: lockshare cacheline: 11281424 usec CPU 0: lockunshare cacheline: 11276093 usec CPU 1: lockunshare cacheline: 11275957 usec [root@virtlab16 testring]# sh run 0 3 CPU 0: share cacheline: 8288335 usec CPU 3: share cacheline: 8288334 usec CPU 0: unshare cacheline: 19107202 usec CPU 3: unshare cacheline: 19107139 usec CPU 0: lockshare cacheline: 11238915 usec CPU 3: lockshare cacheline: 11238848 usec CPU 3: lockunshare cacheline: 11132134 usec CPU 0: lockunshare cacheline: 11132249 usec -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
