On Thu, Aug 13, 2015 at 10:39:19PM -0500, Scott Wood wrote: > On Thu, 2015-08-13 at 19:51 +0800, Kevin Hao wrote: > > I didn't find anything unusual. But I think we do need to order the > > load/store of esel_next when acquire/release tcd lock. For acquire, > > add a data dependency to order the loads of lock and esel_next. > > For release, even there already have a "isync" here, but it doesn't > > guarantee any memory access order. So we still need "lwsync" for > > the two stores for lock and esel_next. > > I was going to say that esel_next is just a hint and it doesn't really matter > if we occasionally get the wrong value, unless it happens often enough to > cause more performance degradation than the lwsync causes. However, with the > A-008139 workaround we do need to read the same value from esel_next both > times. It might be less costly to save/restore an additional register > instead of lwsync, though.
I will try to get some benchmark number to compare which method is a bit better. Do you have any recommended benchmark for a case this is? Thanks, Kevin > > -Scott >
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