linux-kernel - Re: [PATCH 0/2] x86/intel_rdt and perf/x86: Fix lack of coordination with perf

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Date:   Tue, 7 Aug 2018 00:12:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        mingo@...hat.com, fenghua.yu@...el.com, tony.luck@...el.com,
        vikas.shivappa@...ux.intel.com, gavin.hindman@...el.com,
        jithu.joseph@...el.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] x86/intel_rdt and perf/x86: Fix lack of coordination
 with perf

On Mon, Aug 06, 2018 at 12:50:50PM -0700, Reinette Chatre wrote:
> In my previous email I provided the details of the Cache Pseudo-Locking
> feature implemented on top of resctrl. Please let me know if you would
> like any more details about that. I can send you more materials.

I've no yet had time to read..

> BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:748
> 
> I thus continued to use the API with interrupts enabled did the following:
> 
> Two new event attributes:
> static struct perf_event_attr l2_miss_attr = {
>         .type           = PERF_TYPE_RAW,
>         .config         = (0x10ULL << 8) | 0xd1,

Please use something like:

		X86_CONFIG(.event=0xd1, .umask=0x10),

that's ever so much more readable.

>         .size           = sizeof(struct perf_event_attr),
>         .pinned         = 1,
>         .disabled       = 1,
>         .exclude_user   = 1
> };
> 
> static struct perf_event_attr l2_hit_attr = {
>         .type           = PERF_TYPE_RAW,
>         .config         = (0x2ULL << 8) | 0xd1,
>         .size           = sizeof(struct perf_event_attr),
>         .pinned         = 1,
>         .disabled       = 1,
>         .exclude_user   = 1
> };
> 
> Create the two new events using these attributes:
> l2_miss_event = perf_event_create_kernel_counter(&l2_miss_attr, cpu,
> NULL, NULL, NULL);
> l2_hit_event = perf_event_create_kernel_counter(&l2_hit_attr, cpu, NULL,
> NULL, NULL);
> 
> Take measurements:
> perf_event_enable(l2_miss_event);
> perf_event_enable(l2_hit_event);
> local_irq_disable();
> /* Disable hardware prefetchers */
> /* Loop through pseudo-locked memory */
> /* Enable hardware prefetchers */
> local_irq_enable();
> perf_event_disable(l2_hit_event);
> perf_event_disable(l2_miss_event);
> 
> Read results:
> l2_hits = perf_event_read_value(l2_hit_event, &enabled, &running);
> l2_miss = perf_event_read_value(l2_miss_event, &enabled, &running);
> /* Make results available in tracepoints */

switch to .disabled=0 and try this for measurement:

	local_irq_disable();
	perf_event_read_local(l2_miss_event, &miss_val1, NULL, NULL);
	perf_event_read_local(l2_hit_event, &hit_val1, NULL, NULL);
	/* do your thing */
	perf_event_read_local(l2_miss_event, &miss_val2, NULL, NULL);
	perf_event_read_local(l2_hit_event, &hit_val2, NULL, NULL);
	local_irq_enable();

You're running this on the CPU you created the event for, right?

> With the above implementation and a 256KB pseudo-locked memory region I
> obtain the following results:
> pseudo_lock_mea-755   [002] ....   396.946953: pseudo_lock_l2: hits=4140

> The above results are not accurate since it does not reflect the success
> of the pseudo-locked region. Expected results are as we can currently
> obtain (copying results from previous email):
> pseudo_lock_mea-26090 [002] .... 61838.488027: pseudo_lock_l2: hits=4096

Still fairly close.. only like 44 extra hits or 1% error.