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SubjectRe: [PATCH v4 00/10] PCID and improved laziness
On Thu, 29 Jun, at 08:53:12AM, Andy Lutomirski wrote:
> *** Ingo, even if this misses 4.13, please apply the first patch before
> *** the merge window.
>
> There are three performance benefits here:
>
> 1. TLB flushing is slow. (I.e. the flush itself takes a while.)
> This avoids many of them when switching tasks by using PCID. In
> a stupid little benchmark I did, it saves about 100ns on my laptop
> per context switch. I'll try to improve that benchmark.
>
> 2. Mms that have been used recently on a given CPU might get to keep
> their TLB entries alive across process switches with this patch
> set. TLB fills are pretty fast on modern CPUs, but they're even
> faster when they don't happen.
>
> 3. Lazy TLB is way better. We used to do two stupid things when we
> ran kernel threads: we'd send IPIs to flush user contexts on their
> CPUs and then we'd write to CR3 for no particular reason as an excuse
> to stop further IPIs. With this patch, we do neither.

Heads up, I'm gonna queue this for a run on SUSE's performance test
grid.

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