From: Noah Goldstein <goldstein.w.n@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>,
"Carlos O'Donell" <carlos@systemhalted.org>
Subject: Re: [PATCH v4 2/2] x86: Add bounds `x86_non_temporal_threshold`
Date: Wed, 15 Jun 2022 11:33:19 -0700 [thread overview]
Message-ID: <CAFUsyfLJbzaGXUR9Bjxzrfo730vR7Fbp9u46t9tNge3ZJpakNA@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOoh3BiP4ayuRnX7vTYatCrSrt+UN1C4whNoFKKyhSYcOw@mail.gmail.com>
On Wed, Jun 15, 2022 at 11:22 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Wed, Jun 15, 2022 at 10:41 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > The lower-bound (131072) and upper-bound (SIZE_MAX / 16) are assumed
> > by memmove-vec-unaligned-erms.
> >
> > The lower-bound is needed because memmove-vec-unaligned-erms unrolls
> > the loop aggressively in the L(large_memset_4x) case.
> >
> > The upper-bound is needed because memmove-vec-unaligned-erms
> > right-shifts the value of `x86_non_temporal_threshold` by
> > LOG_4X_MEMCPY_THRESH (4) which without a bound may overflow.
> >
> > The lack of lower-bound can be a correctness issue. The lack of
> > upper-bound cannot.
> > ---
> > manual/tunables.texi | 2 +-
> > sysdeps/x86/dl-cacheinfo.h | 6 +++++-
> > 2 files changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/manual/tunables.texi b/manual/tunables.texi
> > index 1482412078..49daf3eb4a 100644
> > --- a/manual/tunables.texi
> > +++ b/manual/tunables.texi
> > @@ -47,7 +47,7 @@ glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0xffffffffffffffff)
> > glibc.elision.skip_lock_busy: 3 (min: -2147483648, max: 2147483647)
> > glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0xffffffffffffffff)
> > glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x1, max: 0xffffffffffffffff)
> > -glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x0, max: 0xffffffffffffffff)
> > +glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x0, max: 0x0fffffffffffffff)
> > glibc.cpu.x86_shstk:
> > glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
> > glibc.malloc.mmap_max: 0 (min: -2147483648, max: 2147483647)
> > diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
> > index cc3b840f9c..f94ff2df43 100644
> > --- a/sysdeps/x86/dl-cacheinfo.h
> > +++ b/sysdeps/x86/dl-cacheinfo.h
> > @@ -931,8 +931,12 @@ 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. Not the '>> 4' also reflect the bound
> > + in the manual. */
> > TUNABLE_SET_WITH_BOUNDS (x86_non_temporal_threshold, non_temporal_threshold,
> > - 0, SIZE_MAX);
> > + 0, SIZE_MAX >> 4);
>
> You didn't change the lower bound.
Fixed in V5.
>
> > 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,
> > --
> > 2.34.1
> >
>
>
> --
> H.J.
next prev parent reply other threads:[~2022-06-15 18:33 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 0:25 [PATCH v1 1/3] x86: Fix misordered logic for setting `rep_movsb_stop_threshold` Noah Goldstein
2022-06-15 0:25 ` [PATCH v1 2/3] x86: Cleanup bounds checking in large memcpy case Noah Goldstein
2022-06-15 1:07 ` H.J. Lu
2022-06-15 3:57 ` Noah Goldstein
2022-06-15 3:57 ` [PATCH v2] " Noah Goldstein
2022-06-15 14:52 ` H.J. Lu
2022-06-15 15:13 ` Noah Goldstein
2022-06-15 15:12 ` [PATCH v3] " Noah Goldstein
2022-06-15 16:48 ` H.J. Lu
2022-06-15 17:44 ` Noah Goldstein
2022-06-15 17:41 ` [PATCH v4 1/2] " Noah Goldstein
2022-06-15 17:41 ` [PATCH v4 2/2] x86: Add bounds `x86_non_temporal_threshold` Noah Goldstein
2022-06-15 18:22 ` H.J. Lu
2022-06-15 18:33 ` Noah Goldstein [this message]
2022-06-15 18:32 ` [PATCH v5 " Noah Goldstein
2022-06-15 18:43 ` H.J. Lu
2022-06-15 19:52 ` [PATCH v6 2/3] " Noah Goldstein
2022-06-15 20:27 ` H.J. Lu
2022-06-15 20:35 ` Noah Goldstein
2022-06-15 20:34 ` [PATCH v7 " Noah Goldstein
2022-06-15 20:48 ` H.J. Lu
2022-07-14 2:55 ` Sunil Pandey
2022-06-15 18:22 ` [PATCH v4 1/2] x86: Cleanup bounds checking in large memcpy case H.J. Lu
2022-07-14 2:57 ` Sunil Pandey
2022-06-15 0:25 ` [PATCH v1 3/3] x86: Add sse42 implementation to strcmp's ifunc Noah Goldstein
2022-06-15 1:08 ` H.J. Lu
2022-07-14 2:54 ` Sunil Pandey
2022-06-15 1:02 ` [PATCH v1 1/3] x86: Fix misordered logic for setting `rep_movsb_stop_threshold` H.J. Lu
2022-07-14 2:53 ` Sunil Pandey
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