From: Noah Goldstein <goldstein.w.n@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH v2] x86: Check minimum/maximum of non_temporal_threshold [BZ #29953]
Date: Tue, 3 Jan 2023 13:15:44 -0800 [thread overview]
Message-ID: <CAFUsyfJJdoAC17qiAHGa4rzeg1+fk7-=ED7MN2R1oq0oNJQ4Rw@mail.gmail.com> (raw)
In-Reply-To: <20230103210648.2569652-1-hjl.tools@gmail.com>
On Tue, Jan 3, 2023 at 1:06 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> The minimum non_temporal_threshold is 0x4040. non_temporal_threshold may
> be set to less than the minimum value when the shared cache size isn't
> available (e.g., in an emulator) or by the tunable. Add checks for
> minimum and maximum of non_temporal_threshold.
>
> This fixes BZ #29953.
> ---
> sysdeps/x86/dl-cacheinfo.h | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
> index e9f3382108..637b5a022d 100644
> --- a/sysdeps/x86/dl-cacheinfo.h
> +++ b/sysdeps/x86/dl-cacheinfo.h
> @@ -861,6 +861,18 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
> share of the cache, it has a substantial risk of negatively
> impacting the performance of other threads running on the chip. */
> unsigned long int non_temporal_threshold = shared * 3 / 4;
> + /* SIZE_MAX >> 4 because memmove-vec-unaligned-erms right-shifts the value of
> + 'x86_non_temporal_threshold' by `LOG_4X_MEMCPY_THRESH` (4) and it is best
> + if that operation cannot overflow. Minimum of 0x4040 (16448) because the
> + L(large_memset_4x) loops need 64-byte to cache align and enough space for
> + at least 1 iteration of 4x PAGE_SIZE unrolled loop. Both values are
> + reflected in the manual. */
> + unsigned long int maximum_non_temporal_threshold = SIZE_MAX >> 4;
> + unsigned long int minimum_non_temporal_threshold = 0x4040;
> + if (non_temporal_threshold < minimum_non_temporal_threshold)
> + non_temporal_threshold = minimum_non_temporal_threshold;
> + else if (non_temporal_threshold > maximum_non_temporal_threshold)
> + non_temporal_threshold = maximum_non_temporal_threshold;
>
> #if HAVE_TUNABLES
> /* NB: The REP MOVSB threshold must be greater than VEC_SIZE * 8. */
> @@ -915,8 +927,8 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
> shared = tunable_size;
>
> tunable_size = TUNABLE_GET (x86_non_temporal_threshold, long int, NULL);
> - /* NB: Ignore the default value 0. */
> - if (tunable_size != 0)
> + if (tunable_size > minimum_non_temporal_threshold
> + && tunable_size <= maximum_non_temporal_threshold)
> non_temporal_threshold = tunable_size;
>
> tunable_size = TUNABLE_GET (x86_rep_movsb_threshold, long int, NULL);
> @@ -931,14 +943,9 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
>
> TUNABLE_SET_WITH_BOUNDS (x86_data_cache_size, data, 0, SIZE_MAX);
> TUNABLE_SET_WITH_BOUNDS (x86_shared_cache_size, shared, 0, SIZE_MAX);
> - /* SIZE_MAX >> 4 because memmove-vec-unaligned-erms right-shifts the value of
> - 'x86_non_temporal_threshold' by `LOG_4X_MEMCPY_THRESH` (4) and it is best
> - if that operation cannot overflow. Minimum of 0x4040 (16448) because the
> - L(large_memset_4x) loops need 64-byte to cache align and enough space for
> - at least 1 iteration of 4x PAGE_SIZE unrolled loop. Both values are
> - reflected in the manual. */
> TUNABLE_SET_WITH_BOUNDS (x86_non_temporal_threshold, non_temporal_threshold,
> - 0x4040, SIZE_MAX >> 4);
> + minimum_non_temporal_threshold,
> + maximum_non_temporal_threshold);
> TUNABLE_SET_WITH_BOUNDS (x86_rep_movsb_threshold, rep_movsb_threshold,
> minimum_rep_movsb_threshold, SIZE_MAX);
> TUNABLE_SET_WITH_BOUNDS (x86_rep_stosb_threshold, rep_stosb_threshold, 1,
> --
> 2.39.0
>
LGTM.
prev parent reply other threads:[~2023-01-03 21:15 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-03 21:06 H.J. Lu
2023-01-03 21:15 ` Noah Goldstein [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAFUsyfJJdoAC17qiAHGa4rzeg1+fk7-=ED7MN2R1oq0oNJQ4Rw@mail.gmail.com' \
--to=goldstein.w.n@gmail.com \
--cc=hjl.tools@gmail.com \
--cc=libc-alpha@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).