This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] Count number of logical processors sharing L2 cache
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 19 May 2016 10:50:31 -0700
- Subject: Re: [PATCH] Count number of logical processors sharing L2 cache
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOoy2YaQTdyqZpQ3=ytDc5dywNshzHAN2ymN60=L5KwbiA at mail dot gmail dot com>
On Fri, May 13, 2016 at 1:39 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>
> We need count number of available logical processors sharing L2
> cache.
For Intel processors, when there are both L2 and L3 caches, SMT level
type should be ued to count number of available logical processors
sharing L2 cache. If there is only L2 cache, core level type should
be used to count number of available logical processors sharing L2
cache. Number of available logical processors sharing L2 cache should
be used for non-inclusive L2 and L3 caches.
Any comments?
--
H.J.
From 5f7d26b9f1d85819700150ea9ee97f46d048ca54 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 13 May 2016 13:26:37 -0700
Subject: [PATCH] Count number of logical processors sharing L2 cache
For Intel processors, when there are both L2 and L3 caches, SMT level
type should be ued to count number of available logical processors
sharing L2 cache. If there is only L2 cache, core level type should
be used to count number of available logical processors sharing L2
cache. Number of available logical processors sharing L2 cache should
be used for non-inclusive L2 and L3 caches.
* sysdeps/x86/cacheinfo.c (init_cacheinfo): Count number of
available logical processors with SMT level type sharing L2
cache for Intel processors.
---
sysdeps/x86/cacheinfo.c | 156 +++++++++++++++++++++++++++++++++++++-----------
1 file changed, 120 insertions(+), 36 deletions(-)
diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c
index 020d3fd..c357bd4 100644
--- a/sysdeps/x86/cacheinfo.c
+++ b/sysdeps/x86/cacheinfo.c
@@ -499,11 +499,24 @@ init_cacheinfo (void)
level = 3;
shared = handle_intel (_SC_LEVEL3_CACHE_SIZE, max_cpuid);
+ /* Number of logical processors sharing L2 cache. */
+ int threads_l2;
+
+ /* Number of logical processors sharing L3 cache. */
+ int threads_l3;
+
if (shared <= 0)
{
/* Try L2 otherwise. */
level = 2;
shared = core;
+ threads_l2 = 0;
+ threads_l3 = -1;
+ }
+ else
+ {
+ threads_l2 = 0;
+ threads_l3 = 0;
}
/* A value of 0 for the HTT bit indicates there is only a single
@@ -519,7 +532,8 @@ init_cacheinfo (void)
int i = 0;
- /* Query until desired cache level is enumerated. */
+ /* Query until cache level 2 and 3 are enumerated. */
+ int check = 0x1 | (threads_l3 == 0) << 1;
do
{
__cpuid_count (4, i++, eax, ebx, ecx, edx);
@@ -530,24 +544,53 @@ init_cacheinfo (void)
assume there is no such information. */
if ((eax & 0x1f) == 0)
goto intel_bug_no_cache_info;
- }
- while (((eax >> 5) & 0x7) != level);
- /* Check if cache is inclusive of lower cache levels. */
- inclusive_cache = (edx & 0x2) != 0;
+ switch ((eax >> 5) & 0x7)
+ {
+ default:
+ break;
+ case 2:
+ if ((check & 0x1))
+ {
+ /* Get maximum number of logical processors
+ sharing L2 cache. */
+ threads_l2 = (eax >> 14) & 0x3ff;
+ check &= ~0x1;
+ }
+ break;
+ case 3:
+ if ((check & (0x1 << 1)))
+ {
+ /* Get maximum number of logical processors
+ sharing L3 cache. */
+ threads_l3 = (eax >> 14) & 0x3ff;
- threads = (eax >> 14) & 0x3ff;
+ /* Check if L2 and L3 caches are inclusive. */
+ inclusive_cache = (edx & 0x2) != 0;
+ check &= ~(0x1 << 1);
+ }
+ break;
+ }
+ }
+ while (check);
- /* If max_cpuid >= 11, THREADS is the maximum number of
- addressable IDs for logical processors sharing the
- cache, instead of the maximum number of threads
+ /* If max_cpuid >= 11, THREADS_L2/THREADS_L3 are the maximum
+ numbers of addressable IDs for logical processors sharing
+ the cache, instead of the maximum number of threads
sharing the cache. */
- if (threads && max_cpuid >= 11)
+ if (max_cpuid >= 11)
{
/* Find the number of logical processors shipped in
one core and apply count mask. */
i = 0;
- while (1)
+
+ /* Count SMT only if there is L3 cache. Always count
+ core if there is no L3 cache. */
+ int count = ((threads_l2 > 0 && level == 3)
+ | ((threads_l3 > 0
+ || (threads_l2 > 0 && level == 2)) << 1));
+
+ while (count)
{
__cpuid_count (11, i++, eax, ebx, ecx, edx);
@@ -555,38 +598,75 @@ init_cacheinfo (void)
int type = ecx & 0xff00;
if (shipped == 0 || type == 0)
break;
+ else if (type == 0x100)
+ {
+ /* Count SMT. */
+ if ((count & 0x1))
+ {
+ int count_mask;
+
+ /* Compute count mask. */
+ asm ("bsr %1, %0"
+ : "=r" (count_mask) : "g" (threads_l2));
+ count_mask = ~(-1 << (count_mask + 1));
+ threads_l2 = (shipped - 1) & count_mask;
+ count &= ~0x1;
+ }
+ }
else if (type == 0x200)
{
- int count_mask;
-
- /* Compute count mask. */
- asm ("bsr %1, %0"
- : "=r" (count_mask) : "g" (threads));
- count_mask = ~(-1 << (count_mask + 1));
- threads = (shipped - 1) & count_mask;
- break;
+ /* Count core. */
+ if ((count & (0x1 << 1)))
+ {
+ int count_mask;
+ int threads_core
+ = (level == 2 ? threads_l2 : threads_l3);
+
+ /* Compute count mask. */
+ asm ("bsr %1, %0"
+ : "=r" (count_mask) : "g" (threads_core));
+ count_mask = ~(-1 << (count_mask + 1));
+ threads_core = (shipped - 1) & count_mask;
+ if (level == 2)
+ threads_l2 = threads_core;
+ else
+ threads_l3 = threads_core;
+ count &= ~(0x1 << 1);
+ }
}
}
}
- threads += 1;
- if (threads > 2 && level == 2 && family == 6)
+ if (threads_l2 > 0)
+ threads_l2 += 1;
+ if (threads_l3 > 0)
+ threads_l3 += 1;
+ if (level == 2)
{
- switch (model)
+ if (threads_l2)
{
- case 0x57:
- /* Knights Landing has L2 cache shared by 2 cores. */
- case 0x37:
- case 0x4a:
- case 0x4d:
- case 0x5a:
- case 0x5d:
- /* Silvermont has L2 cache shared by 2 cores. */
- threads = 2;
- break;
- default:
- break;
+ threads = threads_l2;
+ if (threads > 2 && family == 6)
+ {
+ switch (model)
+ {
+ case 0x57:
+ /* Knights Landing has L2 cache shared by 2 cores. */
+ case 0x37:
+ case 0x4a:
+ case 0x4d:
+ case 0x5a:
+ case 0x5d:
+ /* Silvermont has L2 cache shared by 2 cores. */
+ threads = 2;
+ break;
+ default:
+ break;
+ }
+ }
}
}
+ else if (threads_l3)
+ threads = threads_l3;
}
else
{
@@ -606,8 +686,12 @@ intel_bug_no_cache_info:
}
/* Account for non-inclusive L2 and L3 caches. */
- if (level == 3 && !inclusive_cache)
- shared += core;
+ if (!inclusive_cache)
+ {
+ if (threads_l2 > 0)
+ core /= threads_l2;
+ shared += core;
+ }
}
/* This spells out "AuthenticAMD". */
else if (is_amd)
--
2.5.5