From: Feng Tang <feng.tang@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
kernel test robot <rong.a.chen@intel.com>,
Ingo Molnar <mingo@kernel.org>,
Vince Weaver <vincent.weaver@maine.edu>,
Jiri Olsa <jolsa@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Ravi Bangoria <ravi.bangoria@linux.ibm.com>,
Stephane Eranian <eranian@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, andi.kleen@intel.com, "Huang,
Ying" <ying.huang@intel.com>
Subject: Re: [LKP] Re: [perf/x86] 81ec3f3c4c: will-it-scale.per_process_ops -5.5% regression
Date: Mon, 24 Feb 2020 10:19:15 +0800 [thread overview]
Message-ID: <20200224021915.GC5061@shbuild999.sh.intel.com> (raw)
In-Reply-To: <CAHk-=whi87NNOnNXJ6CvyyedmhnS8dZA2YkQQSajvBArH5XOeA@mail.gmail.com>
On Sun, Feb 23, 2020 at 05:06:33PM -0800, Linus Torvalds wrote:
> > ffffffff8225b580 d types__ptrace
> > ffffffff8225b5c0 D root_user
> > ffffffff8225b680 D init_user_ns
>
> I'm assuming this is after the alignment patch (since that's 64-byte
> aligned there).
>
> What was it without the alignment?
For 5.0-rc6:
ffffffff8225b4c0 d types__ptrace
ffffffff8225b4e0 D root_user
ffffffff8225b580 D init_user_ns
For 5.0-rc6 + 81ec3f3c4c4
ffffffff8225b580 d types__ptrace
ffffffff8225b5a0 D root_user
ffffffff8225b640 D init_user_ns
The sigpending and __count are in the same cachline.
>
> > No, it's not the biggest, I tried another machine 'Xeon Phi(TM) CPU 7295',
> > which has 72C/288T, and the regression is not seen. This is the part
> > confusing me :)
>
> Hmm.
>
> Humor me - what happens if you turn off SMT on that Cascade Lake
> system? Maybe it's about the thread ID bit in the L1? Although again,
> I'd have expected things to get _worse_ if it's the two fields that
> are now in the same cachline thanks to alignment.
I'll try it and report back.
> The Xeon Phi is the small-core setup, right? They may be slow enough
> to not show the issue as clearly despite having more cores. And it
> wouldn't show effects of some out-of-order speculative cache accesses.
Yes, seems the Xeon Phi is using 72 Silvermont cores. And the less bigger
platform I tested was a 2 sockets 48C/96T Cascadelake platform which
doesn't reproduce the regression.
Thanks,
Feng
WARNING: multiple messages have this Message-ID (diff)
From: Feng Tang <feng.tang@intel.com>
To: lkp@lists.01.org
Subject: Re: [perf/x86] 81ec3f3c4c: will-it-scale.per_process_ops -5.5% regression
Date: Mon, 24 Feb 2020 10:19:15 +0800 [thread overview]
Message-ID: <20200224021915.GC5061@shbuild999.sh.intel.com> (raw)
In-Reply-To: <CAHk-=whi87NNOnNXJ6CvyyedmhnS8dZA2YkQQSajvBArH5XOeA@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 1543 bytes --]
On Sun, Feb 23, 2020 at 05:06:33PM -0800, Linus Torvalds wrote:
> > ffffffff8225b580 d types__ptrace
> > ffffffff8225b5c0 D root_user
> > ffffffff8225b680 D init_user_ns
>
> I'm assuming this is after the alignment patch (since that's 64-byte
> aligned there).
>
> What was it without the alignment?
For 5.0-rc6:
ffffffff8225b4c0 d types__ptrace
ffffffff8225b4e0 D root_user
ffffffff8225b580 D init_user_ns
For 5.0-rc6 + 81ec3f3c4c4
ffffffff8225b580 d types__ptrace
ffffffff8225b5a0 D root_user
ffffffff8225b640 D init_user_ns
The sigpending and __count are in the same cachline.
>
> > No, it's not the biggest, I tried another machine 'Xeon Phi(TM) CPU 7295',
> > which has 72C/288T, and the regression is not seen. This is the part
> > confusing me :)
>
> Hmm.
>
> Humor me - what happens if you turn off SMT on that Cascade Lake
> system? Maybe it's about the thread ID bit in the L1? Although again,
> I'd have expected things to get _worse_ if it's the two fields that
> are now in the same cachline thanks to alignment.
I'll try it and report back.
> The Xeon Phi is the small-core setup, right? They may be slow enough
> to not show the issue as clearly despite having more cores. And it
> wouldn't show effects of some out-of-order speculative cache accesses.
Yes, seems the Xeon Phi is using 72 Silvermont cores. And the less bigger
platform I tested was a 2 sockets 48C/96T Cascadelake platform which
doesn't reproduce the regression.
Thanks,
Feng
next prev parent reply other threads:[~2020-02-24 2:19 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 12:32 [perf/x86] 81ec3f3c4c: will-it-scale.per_process_ops -5.5% regression kernel test robot
2020-02-05 12:32 ` kernel test robot
2020-02-05 12:58 ` Peter Zijlstra
2020-02-05 12:58 ` Peter Zijlstra
2020-02-06 3:04 ` [LKP] " Li, Philip
2020-02-06 3:04 ` Li, Philip
2020-02-21 8:03 ` [LKP] " Feng Tang
2020-02-21 8:03 ` Feng Tang
2020-02-21 10:58 ` [LKP] " Peter Zijlstra
2020-02-21 10:58 ` Peter Zijlstra
2020-02-21 13:20 ` [LKP] " Jiri Olsa
2020-02-21 13:20 ` Jiri Olsa
2020-02-23 14:11 ` [LKP] " Feng Tang
2020-02-23 14:11 ` Feng Tang
2020-02-23 17:37 ` [LKP] " Linus Torvalds
2020-02-23 17:37 ` Linus Torvalds
2020-02-24 0:33 ` [LKP] " Feng Tang
2020-02-24 0:33 ` Feng Tang
2020-02-24 1:06 ` [LKP] " Linus Torvalds
2020-02-24 1:06 ` Linus Torvalds
2020-02-24 1:58 ` [LKP] " Huang, Ying
2020-02-24 1:58 ` Huang, Ying
2020-02-24 2:19 ` Feng Tang [this message]
2020-02-24 2:19 ` Feng Tang
2020-02-24 13:20 ` [LKP] " Feng Tang
2020-02-24 13:20 ` Feng Tang
2020-02-24 19:24 ` [LKP] " Linus Torvalds
2020-02-24 19:24 ` Linus Torvalds
2020-02-24 19:42 ` [LKP] " Kleen, Andi
2020-02-24 19:42 ` Kleen, Andi
2020-02-24 20:09 ` [LKP] " Linus Torvalds
2020-02-24 20:09 ` Linus Torvalds
2020-02-24 20:47 ` [LKP] " Linus Torvalds
2020-02-24 20:47 ` Linus Torvalds
2020-02-24 21:20 ` [LKP] " Eric W. Biederman
2020-02-24 21:20 ` Eric W. Biederman
2020-02-24 21:43 ` [LKP] " Linus Torvalds
2020-02-24 21:43 ` Linus Torvalds
2020-02-24 21:59 ` [LKP] " Eric W. Biederman
2020-02-24 21:59 ` Eric W. Biederman
2020-02-24 22:12 ` [LKP] " Linus Torvalds
2020-02-24 22:12 ` Linus Torvalds
2020-02-25 2:57 ` [LKP] " Feng Tang
2020-02-25 2:57 ` Feng Tang
2020-02-25 3:15 ` [LKP] " Linus Torvalds
2020-02-25 3:15 ` Linus Torvalds
2020-02-25 4:53 ` [LKP] " Feng Tang
2020-02-25 4:53 ` Feng Tang
2020-02-23 19:36 ` [LKP] " Jiri Olsa
2020-02-23 19:36 ` Jiri Olsa
2020-02-24 1:14 ` Feng Tang
2020-02-21 18:05 ` [LKP] " Kleen, Andi
2020-02-21 18:05 ` Kleen, Andi
2020-02-22 12:43 ` [LKP] " Feng Tang
2020-02-22 12:43 ` Feng Tang
2020-02-22 17:08 ` [LKP] " Kleen, Andi
2020-02-22 17:08 ` Kleen, Andi
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