Messages in this thread | | | Date | Mon, 6 May 2024 22:17:41 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v4 1/5] x86/bugs: Only harden syscalls when needed |
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On Mon, Apr 22, 2024 at 04:09:33PM +0800, Yujie Liu wrote: > On Fri, Apr 19, 2024 at 02:09:47PM -0700, Josh Poimboeuf wrote: > > Syscall hardening (converting the syscall indirect branch to a series of > > direct branches) has shown some performance regressions: > > > > - Red Hat internal testing showed up to 12% slowdowns in database > > benchmark testing on Sapphire Rapids when the DB was stressed with 80+ > > users to cause contention. > > > > - The kernel test robot's will-it-scale benchmarks showed significant > > regressions on Skylake with IBRS: > > https://lkml.kernel.org/lkml/202404191333.178a0eed-yujie.liu@intel.com > > To clarify, we reported a +1.4% improvement (not regression) of > will-it-scale futex4 benchmark on Skylake. Meanwhile we did observe some > regressions by running other benchmarks on Ice Lake, such as: > > stress-ng.null.ops_per_sec -4.0% regression on Intel Xeon Gold 6346 (Ice Lake) > unixbench.fsbuffer.throughput -1.4% regression on Intel Xeon Gold 6346 (Ice Lake)
Thanks for clarifying that. I'm not sure what I was looking at.
I also saw your email where Ice Lake showed a ~10% regression for 1e3ad78334a6. Unfortunately my patch wouldn't help with that, as it's designed to help with older systems (e.g., Skylake) and newer (e.g., Sapphire Rapids) but not Ice/Cascade Lake.
Whether 1e3ad78334a6 helps or hurts seems very workload-dependent.
It would be especially interesting to see if my patch helps on the newer systems which have the HW mitigation: Raptor Lake, Meteor Lake, Sapphire Rapids, Emerald Rapids.
For now, maybe I'll just table this patch until we have more data.
-- Josh
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