[pushed] linux: Add comment on affinity set sizes to tst-skeleton-affinity.c
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Message ID 20191115123020.E3AB320AF6@gnutoolchain-gerrit.osci.io
State New
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  • [pushed] linux: Add comment on affinity set sizes to tst-skeleton-affinity.c
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Commit Message

Adhemerval Zanella (Code Review) Nov. 15, 2019, 12:30 p.m. UTC
Sourceware to Gerrit sync has submitted this change.

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/glibc/+/610
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linux: Add comment on affinity set sizes to tst-skeleton-affinity.c

Change-Id: Ic6ec48f75f3a0576d3121befd04531382c92afb4
---
M sysdeps/unix/sysv/linux/tst-skeleton-affinity.c
1 file changed, 5 insertions(+), 0 deletions(-)

Approvals:
  Szabolcs Nagy: Looks good to me, approved

Patch
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diff --git a/sysdeps/unix/sysv/linux/tst-skeleton-affinity.c b/sysdeps/unix/sysv/linux/tst-skeleton-affinity.c
index 32fb94c..9d1f27f 100644
--- a/sysdeps/unix/sysv/linux/tst-skeleton-affinity.c
+++ b/sysdeps/unix/sysv/linux/tst-skeleton-affinity.c
@@ -264,6 +264,11 @@ 
 
   struct conf conf;
   setup_conf (&conf);
+  /* Note: The CPU set size in bits can be less than the CPU count
+     (and the maximum test CPU) because the userspace interface rounds
+     up the bit count, and the rounded-up buffer size is passed into
+     the kernel.  The kernel does not know that some of the buffer are
+     actually padding, and writes data there.  */
   printf ("info: Detected CPU set size (in bits): %d\n", conf.set_size);
   printf ("info: Maximum test CPU: %d\n", conf.last_cpu);
   if (conf.set_size < 0 || conf.last_cpu < 0)