4 ms·
This is a huge performance hit - up to 50% it is claimed! 70% of modern intel processors are affected apparently as well.
by buildbot 3y ago
This is a huge performance hit - up to 50% it is claimed!
70% of modern intel processors are affected apparently as well.
- samwillis 3y ago> some workloads may experience up to 50% overhead They word there are "some workloads", I suspect that performance hit is rare.
- jgtrosh 3y agoMy guess is that HPC systems which run applications whose performance strongly depends on efficient data scatter gather will immediately disable the mitigation.
- loeg 3y agoKey context you elided: "This depends on whether Gather is in the critical execution path of a program."
- buildbot 3y agoWell yes. That is the up to part.
- ablated_maquis 3y agoIs that 50% overhead for "Gather" instructions? If that is the case, then if 10% of instructions are "gathers" in your workload then that would be 5% overall.
- loeg 3y agoSomething like that, yeah.
- dralley 3y ago"Red Hat’s internal performance testing of a worst-case microbenchmark showed a significant slowdown. However, more realistic applications that utilize vector gathering showed only low single-digit percentage slowdowns." https://access.redhat.com/solutions/7027704 https://access.redhat.com/solutions/7027704 Performance Impact The performance impact of the microcode mitigation is limited to applications that use the gather instructions provided by Intel Advanced Vector Extensions (AVX2 and AVX-512) and the CLWB instruction. Actual performance impact will depend on how heavily an application uses those instructions. Red Hat’s internal performance testing of a worst-case microbenchmark showed a significant slowdown. However, more realistic applications that utilize vector gathering showed only low single-digit percentage slowdowns. If the user decides to disable the mitigation after doing a thorough risk analysis (for example the system isn’t multi-tenant and doesn’t execute untrusted code), the user can disable the mitigation. After applying the microcode and kernel updates, the user can disable the mitigation by adding gather_data_samping=off to the kernel command line.Alternatively, to disable all CPU speculative execution mitigations, including GDS, use mitigations=off.
- graton 3y agoIt is kind of like thinking that it is a huge sale at a store when they say "Up to 70% off". And there are like two things in the whole store which are 70% off. I am always suspicious of "up to" claims.
- IlliOnato 3y agoI always translate such weasel words to their more straightforward equivalent. "Up to 70% off" means for me "Nothing in our store is discounted by more than 70%" :-)
- deleted 3y ago[deleted]