Re: [PATCH 16/28] x86/intel_rdt: Prepare to add RDT monitor cpus file support

From: Shivappa Vikas
Date: Tue Aug 01 2017 - 17:33:18 EST

On Tue, 1 Aug 2017, Thomas Gleixner wrote:

On Tue, 25 Jul 2017, Vikas Shivappa wrote:
* The cached intel_pqr_state is strictly per CPU and can never be
* updated from a remote CPU. Functions which modify the state
@@ -49,6 +47,8 @@
DEFINE_PER_CPU(struct intel_pqr_state, pqr_state);

+DEFINE_PER_CPU_READ_MOSTLY(struct intel_pqr_state, rdt_cpu_default);

Cacheline wise this is suboptimal. You have to touch two cachelines on each
context switch (at least for read).

If you make that:

struct intel_pqr_state {
u32 default_cosid;
u32 default_rmid;
u32 cur_cosid;
u32 cur_rmid;

DEFINE_PER_CPU(struct intel_pqr_state, pqr_state);

then it's all together and you spare one cache line.

Will fix..