On 10/15/21 4:44 AM, tip-bot2 for Tim Chen wrote:
The following commit has been merged into the sched/core branch of tip: Commit-ID: 66558b730f2533cc2bf2b74d51f5f80b81e2bad0 Gitweb: https://git.kernel.org/tip/66558b730f2533cc2bf2b74d51f5f80b81e2bad0 Author: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> AuthorDate: Fri, 24 Sep 2021 20:51:04 +12:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Fri, 15 Oct 2021 11:25:16 +02:00 sched: Add cluster scheduler level for x86 There are x86 CPU architectures (e.g. Jacobsville) where L2 cahce is shared among a cluster of cores instead of being exclusive to one single core. To prevent oversubscription of L2 cache, load should be balanced between such L2 clusters, especially for tasks with no shared data. On benchmark such as SPECrate mcf test, this change provides a boost to performance especially on medium load system on Jacobsville. on a Jacobsville that has 24 Atom cores, arranged into 6 clusters of 4 cores each, the benchmark number is as follow: Improvement over baseline kernel for mcf_r copies run time base rate 1 -0.1% -0.2% 6 25.1% 25.1% 12 18.8% 19.0% 24 0.3% 0.3% So this looks pretty good. In terms of the system's task distribution, some pretty bad clumping can be seen for the vanilla kernel without the L2 cluster domain for the 6 and 12 copies case. With the extra domain for cluster, the load does get evened out between the clusters. Note this patch isn't an universal win as spreading isn't necessarily a win, particually for those workload who can benefit from packing. Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210924085104.44806-4-21cnbao@xxxxxxxxx
I've bisected to this patch which now results in my EPYC systems issuing a lot of:
[ 4.788480] BUG: arch topology borken [ 4.789578] the SMT domain not a subset of the CLS domain messages (one for each CPU in the system).I haven't had a chance to dig deeper and understand everything, does anyone have some quick insights/ideas?
Thanks, Tom
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