46 lines
2.1 KiB
Diff
46 lines
2.1 KiB
Diff
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From ed2f9dc9420c4c61436328778a70459d0a35556a Mon Sep 17 00:00:00 2001
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From: Noah Goldstein <goldstein.w.n@gmail.com>
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Date: Mon, 8 May 2023 22:10:20 -0500
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Subject: [PATCH] x86: Use 64MB as nt-store threshold if no cacheinfo [BZ
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#30429]
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Content-type: text/plain; charset=UTF-8
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If `non_temporal_threshold` is below `minimum_non_temporal_threshold`,
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it almost certainly means we failed to read the systems cache info.
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In this case, rather than defaulting the minimum correct value, we
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should default to a value that gets at least reasonable
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performance. 64MB is chosen conservatively to be at the very high
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end. This should never cause non-temporal stores when, if we had read
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cache info, we wouldn't have otherwise.
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Reviewed-by: Florian Weimer <fweimer@redhat.com>
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---
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sysdeps/x86/dl-cacheinfo.h | 10 +++++++++-
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1 file changed, 9 insertions(+), 1 deletion(-)
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diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
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index ec88945b39..877e73d700 100644
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--- a/sysdeps/x86/dl-cacheinfo.h
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+++ b/sysdeps/x86/dl-cacheinfo.h
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@@ -749,8 +749,16 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
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reflected in the manual. */
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unsigned long int maximum_non_temporal_threshold = SIZE_MAX >> 4;
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unsigned long int minimum_non_temporal_threshold = 0x4040;
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+
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+ /* If `non_temporal_threshold` less than `minimum_non_temporal_threshold`
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+ it most likely means we failed to detect the cache info. We don't want
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+ to default to `minimum_non_temporal_threshold` as such a small value,
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+ while correct, has bad performance. We default to 64MB as reasonable
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+ default bound. 64MB is likely conservative in that most/all systems would
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+ choose a lower value so it should never forcing non-temporal stores when
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+ they otherwise wouldn't be used. */
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if (non_temporal_threshold < minimum_non_temporal_threshold)
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- non_temporal_threshold = minimum_non_temporal_threshold;
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+ non_temporal_threshold = 64 * 1024 * 1024;
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else if (non_temporal_threshold > maximum_non_temporal_threshold)
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non_temporal_threshold = maximum_non_temporal_threshold;
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--
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2.39.3
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