Messages in this thread | | | Date | Wed, 4 Oct 2023 12:11:04 -0400 | Subject | Re: [PATCH v6 0/4] x86/speculation: Disable IBRS when idle | From | Waiman Long <> |
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On 10/4/23 07:50, Ingo Molnar wrote: > * Waiman Long <longman@redhat.com> wrote: > >> For Intel processors that need to turn on IBRS to protect against >> Spectre v2 and Retbleed, the IBRS bit in the SPEC_CTRL MSR affects >> the performance of the whole core even if only one thread is turning >> it on when running in the kernel. For user space heavy applications, >> the performance impact of occasionally turning IBRS on during syscalls >> shouldn't be significant. Unfortunately, that is not the case when the >> sibling thread is idling in the kernel. In that case, the performance >> impact can be significant. >> >> When DPDK is running on an isolated CPU thread processing network packets >> in user space while its sibling thread is idle. The performance of the >> busy DPDK thread with IBRS on and off in the sibling idle thread are: >> >> IBRS on IBRS off >> ------- -------- >> packets/second: 7.8M 10.4M >> avg tsc cycles/packet: 282.26 209.86 >> >> This is a 25% performance degradation. The test system is a Intel Xeon >> 4114 CPU @ 2.20GHz. > Ok, that's a solid improvement, and the feature has no obvious > downsides, so I've applied your series to tip:sched/core with a few > edits here and there.
Thanks!
-Longman
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