From: Thomas Rodgers <trodgers@redhat.com>
To: "libstdc++" <libstdc++@gcc.gnu.org>,
gcc Patches <gcc-patches@gcc.gnu.org>
Subject: libstdc++: Minor codegen improvement for atomic wait spinloop
Date: Tue, 5 Jul 2022 18:04:42 -0700 [thread overview]
Message-ID: <CAMmuTO9uSsBB7vVrAEFK60vCFwC67yTRNeC_EtMNiUCquy0=gQ@mail.gmail.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 203 bytes --]
This patch merges the spin loops in the atomic wait implementation which is
a
minor codegen improvement.
libstdc++-v3/ChangeLog:
* include/bits/atomic_wait.h (__atomic_spin): Merge spin loops.
[-- Attachment #2: 0001-libstdc-Minor-codegen-improvement-for-atomic-wait-sp.patch --]
[-- Type: application/octet-stream, Size: 1726 bytes --]
From 5bd6b6f0e7d630c597900e82fe04bb2bc7a1e3d4 Mon Sep 17 00:00:00 2001
From: Thomas Rodgers <trodgers@redhat.com>
Date: Tue, 5 Jul 2022 17:42:42 -0700
Subject: [PATCH] libstdc++: Minor codegen improvement for atomic wait spinloop
This patch merges the spin loops in the atomic wait implementation which is a
minor codegen improvement.
libstdc++-v3/ChangeLog:
* include/bits/atomic_wait.h (__atomic_spin): Merge spin loops.
---
libstdc++-v3/include/bits/atomic_wait.h | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 125b1cad886..a6d55d3af8a 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -142,8 +142,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif
}
- constexpr auto __atomic_spin_count_1 = 12;
- constexpr auto __atomic_spin_count_2 = 4;
+ constexpr auto __atomic_spin_count_relax = 12;
+ constexpr auto __atomic_spin_count = 16;
struct __default_spin_policy
{
@@ -157,18 +157,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool
__atomic_spin(_Pred& __pred, _Spin __spin = _Spin{ }) noexcept
{
- for (auto __i = 0; __i < __atomic_spin_count_1; ++__i)
+ for (auto __i = 0; __i < __atomic_spin_count; ++__i)
{
if (__pred())
return true;
- __detail::__thread_relax();
- }
- for (auto __i = 0; __i < __atomic_spin_count_2; ++__i)
- {
- if (__pred())
- return true;
- __detail::__thread_yield();
+ if (__i < __atomic_spin_count_relax)
+ __detail::__thread_relax();
+ else
+ __detail::__thread_yield();
}
while (__spin())
--
2.36.1
next reply other threads:[~2022-07-06 1:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-06 1:04 Thomas Rodgers [this message]
2022-07-06 20:56 ` Jonathan Wakely
2022-07-06 21:41 ` Thomas Rodgers
2022-07-07 9:30 ` Jonathan Wakely
2022-07-26 22:42 ` Thomas Rodgers
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='CAMmuTO9uSsBB7vVrAEFK60vCFwC67yTRNeC_EtMNiUCquy0=gQ@mail.gmail.com' \
--to=trodgers@redhat.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=libstdc++@gcc.gnu.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).