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From:   Matteo Rizzo <matteorizzo@google.com>
Date:   Tue, 19 Sep 2023 15:42:47 +0200
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Subject: Re: [RFC PATCH 00/14] Prevent cross-cache attacks in the SLUB allocator
To:     Ingo Molnar <mingo@kernel.org>
Cc:     "Lameter, Christopher" <cl@os.amperecomputing.com>,
        Dave Hansen <dave.hansen@intel.com>, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com,
        akpm@linux-foundation.org, vbabka@suse.cz,
        roman.gushchin@linux.dev, 42.hyeyoo@gmail.com,
        keescook@chromium.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-hardening@vger.kernel.org, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        x86@kernel.org, hpa@zytor.com, corbet@lwn.net, luto@kernel.org,
        peterz@infradead.org, jannh@google.com, evn@google.com,
        poprdi@google.com, jordyzomer@google.com,
        Linus Torvalds <torvalds@linux-foundation.org>
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On Mon, 18 Sept 2023 at 19:39, Ingo Molnar <mingo@kernel.org> wrote:
>
> What's the split of the increase in overhead due to SLAB_VIRTUAL=y, between
> user-space execution and kernel-space execution?
>

Same benchmark as before (compiling a kernel on a system running the patched
kernel):

Intel Skylake:

      LABEL    | COUNT |   MIN    |   MAX    |   MEAN   |  MEDIAN  | STDDEV
---------------+-------+----------+----------+----------+----------+--------
wall clock     |       |          |          |          |          |
SLAB_VIRTUAL=n | 150   | 49.700   | 51.320   | 50.449   | 50.430   | 0.29959
SLAB_VIRTUAL=y | 150   | 50.020   | 51.660   | 50.880   | 50.880   | 0.30495
               |       | +0.64%   | +0.66%   | +0.85%   | +0.89%   | +1.79%
system time    |       |          |          |          |          |
SLAB_VIRTUAL=n | 150   | 358.560  | 362.900  | 360.922  | 360.985  | 0.91761
SLAB_VIRTUAL=y | 150   | 362.970  | 367.970  | 366.062  | 366.115  | 1.015
               |       | +1.23%   | +1.40%   | +1.42%   | +1.42%   | +10.60%
user time      |       |          |          |          |          |
SLAB_VIRTUAL=n | 150   | 3110.000 | 3124.520 | 3118.143 | 3118.120 | 2.466
SLAB_VIRTUAL=y | 150   | 3115.070 | 3127.070 | 3120.762 | 3120.925 | 2.654
               |       | +0.16%   | +0.08%   | +0.08%   | +0.09%   | +7.63%

AMD Milan:

      LABEL    | COUNT |   MIN    |   MAX    |   MEAN   |  MEDIAN  | STDDEV
---------------+-------+----------+----------+----------+----------+--------
wall clock     |       |          |          |          |          |
SLAB_VIRTUAL=n | 150   | 25.480   | 26.550   | 26.065   | 26.055   | 0.23495
SLAB_VIRTUAL=y | 150   | 25.820   | 27.080   | 26.531   | 26.540   | 0.25974
               |       | +1.33%   | +2.00%   | +1.79%   | +1.86%   | +10.55%
system time    |       |          |          |          |          |
SLAB_VIRTUAL=n | 150   | 478.530  | 540.420  | 520.803  | 521.485  | 9.166
SLAB_VIRTUAL=y | 150   | 530.520  | 572.460  | 552.825  | 552.985  | 7.161
               |       | +10.86%  | +5.93%   | +6.15%   | +6.04%   | -21.88%
user time      |       |          |          |          |          |
SLAB_VIRTUAL=n | 150   | 2373.540 | 2403.800 | 2386.343 | 2385.840 | 5.325
SLAB_VIRTUAL=y | 150   | 2388.690 | 2426.290 | 2408.325 | 2408.895 | 6.667
               |       | +0.64%   | +0.94%   | +0.92%   | +0.97%   | +25.20%


I'm not exactly sure why user time increases by almost 1% on Milan, it could be
TLB contention.

--
Matteo