Re: [PATCH 0/9] Performance-related backports for 4.12

[Greg KH <gregkh@linuxfoundation.org>]

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...