On Mon, Jul 10, 2017 at 01:37:43PM +0100, Mel Gorman wrote: > The 4.12 release was large but there was a number of important > performance-related patches that are relatively low-hanging fruit. There > are other patches but data is still being collected. This is a collection > that have only been tested on 4.12 and while they may merge against older > kernels, I have no data on how it behaves and cannot guarantee it's a good > idea so I don't recommend it. > > Patch 1 is an x86 microoptimisation for processors with ERMS. The improvement > is marginal with effects often within the noise but it's a small > boost on syscall-intensive workloads that move a lot of data > to userspace. > > Patches 2-3 reworks select_idle_cpu, particularly around idle scanning to > use a limited scan instead of a complete cut-off. The boost for > hackbench is variable with an old machine with limited CPUs only > getting a 3-4% boost while a larger 2-socket machine with 48 cores > saw a 7-20% boost for low thread counts and no difference when > the machine was saturated. Other workloads that are not as > wakeup intensive barely notice which is to be expected. > > Patch 4 addresses a soft lockup that was detected on a memory-intensive > workload with large numbers of threads and NUMA balancing > implemented. While I personally cannot verify the fix as the > workload in question is not available, I know it was confirmed > to work by a user. > > Patches 5-9 addresses a number of problems with automatic NUMA balancing. > While the patch author said that there was a big boost on specjbb and > NAS, this was on a 4-socket machine in a ring topology and I don't > have access to a similar machine. However, on a 2-socket machine, > there was a 5% boost to specjbb 2005 when running a single JVM > and a 1-2% boost when using multiple JVMs. There was little or no > difference to NAS on the same machine but this may be due to the > fact it's a 2-socket machine and a relatively short-lived workload. > It's also known to boost hackbench on some machines by roughly 20%. Thanks for these, I've queued them all up now. I couldn't resist patch 1 for the older kernels as well, can't hurt[1] :) thanks, greg k-h [1] Famous last words...