From: Michael Ellerman <mpe@ellerman•id.au>
To: Kajol Jain <kjain@linux•ibm.com>,
linuxppc-dev@lists•ozlabs.org, linux-kernel@vger•kernel.org,
peterz@infradead•org, mingo@redhat•com, acme@kernel•org,
jolsa@kernel•org, namhyung@kernel•org,
linux-perf-users@vger•kernel.org, ak@linux•intel.com
Cc: mark.rutland@arm•com, songliubraving@fb•com,
atrajeev@linux•vnet.ibm.com, daniel@iogearbox•net,
rnsastry@linux•ibm.com, alexander.shishkin@linux•intel.com,
kjain@linux•ibm.com, ast@kernel•org, yao.jin@linux•intel.com,
maddy@linux•ibm.com, paulus@samba•org, kan.liang@linux•intel.com
Subject: Re: [PATCH 1/3] perf: Add macros to specify onchip L2/L3 accesses
Date: Wed, 08 Sep 2021 17:17:53 +1000 [thread overview]
Message-ID: <87ilzbmt7i.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20210904064932.307610-1-kjain@linux.ibm.com>
Kajol Jain <kjain@linux•ibm.com> writes:
> Add couple of new macros to represent onchip L2 and onchip L3 accesses.
It would be "on chip". But I think this needs much more explanation,
this is a generic header so these definitions need to make sense, and
have an understood meaning, across all architectures.
I think most people are going to read "on chip" as differentiating
between an L2/L3 that is "on chip" vs "off chip".
But the case you're trying to express is "another core's L2/L3 on the
same chip as the CPU", vs "the current CPU's L2/L3".
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index f92880a15645..030b3e990ac3 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -1265,7 +1265,9 @@ union perf_mem_data_src {
> #define PERF_MEM_LVLNUM_L2 0x02 /* L2 */
> #define PERF_MEM_LVLNUM_L3 0x03 /* L3 */
> #define PERF_MEM_LVLNUM_L4 0x04 /* L4 */
> -/* 5-0xa available */
> +#define PERF_MEM_LVLNUM_OC_L2 0x05 /* On Chip L2 */
> +#define PERF_MEM_LVLNUM_OC_L3 0x06 /* On Chip L3 */
The obvious use for 5 is for "L5" and so on.
I'm not sure adding new levels is the best idea, because these don't fit
neatly into the hierarchy, they are off to the side.
I wonder if we should use the remote field.
ie. for another core's L2 we set:
mem_lvl = PERF_MEM_LVL_L2
mem_remote = 1
Which would mean "remote L2", but not remote enough to be
lvl = PERF_MEM_LVL_REM_CCE1.
It would be printed by the existing tools/perf code as "Remote L2", vs
"Remote cache (1 hop)", which seems OK.
ie. we'd be able to express:
Current core's L2: LVL_L2
Other core's L2: LVL_L2 | REMOTE
Other chip's L2: LVL_REM_CCE1 | REMOTE
And similarly for L3.
I think that makes sense? Unless people think remote should be reserved
to mean on another chip, though we already have REM_CCE1 for that.
cheers
next prev parent reply other threads:[~2021-09-08 7:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-04 6:49 [PATCH 1/3] perf: Add macros to specify onchip L2/L3 accesses Kajol Jain
2021-09-04 6:49 ` [PATCH 2/3] " Kajol Jain
2021-09-04 6:49 ` [PATCH 3/3] powerpc/perf: Fix data source encodings for power10 Kajol Jain
2021-09-08 7:17 ` Michael Ellerman [this message]
2021-09-08 9:26 ` [PATCH 1/3] perf: Add macros to specify onchip L2/L3 accesses Peter Zijlstra
2021-09-09 12:45 ` Michael Ellerman
2021-09-09 14:36 ` Peter Zijlstra
2021-09-14 10:40 ` Michael Ellerman
2021-09-14 11:49 ` Peter Zijlstra
2021-09-16 10:57 ` Michael Ellerman
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