On Fri, 30 Jun, at 01:44:22PM, Matt Fleming wrote: > 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.
FWIW, I didn't see any change in performance with this series on a PCID-capable machine. On the plus side, I didn't see any weird-looking bugs either. Are your benchmarks available anywhere?
