Messages in this thread | | | Date | Mon, 10 Feb 2014 22:18:25 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 00/21] perf, c2c: Add new tool to analyze cacheline contention on NUMA systems |
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On Mon, Feb 10, 2014 at 12:28:55PM -0500, Don Zickus wrote: > With the introduction of NUMA systems, came the possibility of remote memory accesses. > Combine those remote memory accesses with contention on the remote node (ie a modified > cacheline) and you have a possibility for very long latencies. These latencies can > bottleneck a program. > > The program added by these patches, helps detect the situation where two nodes are > 'tugging' on the same _data_ cacheline. The term used through out this program and > the various changelogs is called a HITM. This means nodeX went to read a cacheline > and it was discovered to be loaded in nodeY's LLC cache (hence the cacheHIT). The > remote cacheline was also in a 'M'odified state thus creating a 'HIT M' for hit in > a modified state. HITMs can happen locally and remotely. This program's interest > is mainly in remote HITMs as they cause the longest latencies.
All of that is true of the traditional SMP system too. Just use lower level caches.
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