Why doesn't glib use private futexes?
up vote
4
down vote
favorite
When investigating some performance issues, I finally ended up in gthread-posix.c.
There I found code such as:
static void __attribute__((noinline))
g_mutex_lock_slowpath (GMutex *mutex)
{
/* Set to 2 to indicate contention. If it was zero before then we
* just acquired the lock.
*
* Otherwise, sleep for as long as the 2 remains...
*/
while (exchange_acquire (&mutex->i[0], 2) != 0)
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT, (gsize) 2, NULL);
}
I am curious as to why it doesn't use FUTEX_WAIT_PRIVATE here and it other places. At least on the ARM the non-private futexes are significantly slower, and I was under the impression that glib is for multithreading rather than interprocess communication in shared memory.
glib futex
asked Mar 6 '15 at 9:46
Jan Nordén
312
add a comment |
up vote
4
down vote
favorite
When investigating some performance issues, I finally ended up in gthread-posix.c.
There I found code such as:
static void __attribute__((noinline))
g_mutex_lock_slowpath (GMutex *mutex)
{
/* Set to 2 to indicate contention. If it was zero before then we
* just acquired the lock.
*
* Otherwise, sleep for as long as the 2 remains...
*/
while (exchange_acquire (&mutex->i[0], 2) != 0)
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT, (gsize) 2, NULL);
}
I am curious as to why it doesn't use FUTEX_WAIT_PRIVATE here and it other places. At least on the ARM the non-private futexes are significantly slower, and I was under the impression that glib is for multithreading rather than interprocess communication in shared memory.
glib futex
asked Mar 6 '15 at 9:46
Jan Nordén
312
Perhaps bug glibc mailing list re: lwn.net/Articles/229668 ? I imagine it was already discussed....
– Dima Tisnek
Feb 8 '16 at 9:54
add a comment |
up vote
4
down vote
favorite
up vote
4
down vote
favorite
When investigating some performance issues, I finally ended up in gthread-posix.c.
There I found code such as:
static void __attribute__((noinline))
g_mutex_lock_slowpath (GMutex *mutex)
{
/* Set to 2 to indicate contention. If it was zero before then we
* just acquired the lock.
*
* Otherwise, sleep for as long as the 2 remains...
*/
while (exchange_acquire (&mutex->i[0], 2) != 0)
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT, (gsize) 2, NULL);
}
I am curious as to why it doesn't use FUTEX_WAIT_PRIVATE here and it other places. At least on the ARM the non-private futexes are significantly slower, and I was under the impression that glib is for multithreading rather than interprocess communication in shared memory.
glib futex
asked Mar 6 '15 at 9:46
Jan Nordén
312
When investigating some performance issues, I finally ended up in gthread-posix.c.
There I found code such as:
static void __attribute__((noinline))
g_mutex_lock_slowpath (GMutex *mutex)
{
/* Set to 2 to indicate contention. If it was zero before then we
* just acquired the lock.
*
* Otherwise, sleep for as long as the 2 remains...
*/
while (exchange_acquire (&mutex->i[0], 2) != 0)
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT, (gsize) 2, NULL);
}
I am curious as to why it doesn't use FUTEX_WAIT_PRIVATE here and it other places. At least on the ARM the non-private futexes are significantly slower, and I was under the impression that glib is for multithreading rather than interprocess communication in shared memory.
glib futex
glib futex
asked Mar 6 '15 at 9:46
Jan Nordén
312
asked Mar 6 '15 at 9:46
Jan Nordén
312
asked Mar 6 '15 at 9:46
Jan Nordén
312
asked Mar 6 '15 at 9:46
Jan Nordén
312
asked Mar 6 '15 at 9:46
Jan Nordén
312
312
Perhaps bug glibc mailing list re: lwn.net/Articles/229668 ? I imagine it was already discussed....
– Dima Tisnek
Feb 8 '16 at 9:54
add a comment |
Perhaps bug glibc mailing list re: lwn.net/Articles/229668 ? I imagine it was already discussed....
– Dima Tisnek
Feb 8 '16 at 9:54
Perhaps bug glibc mailing list re: lwn.net/Articles/229668 ? I imagine it was already discussed....
– Dima Tisnek
Feb 8 '16 at 9:54
Perhaps bug glibc mailing list re: lwn.net/Articles/229668 ? I imagine it was already discussed....
– Dima Tisnek
Feb 8 '16 at 9:54
add a comment |
1 Answer
1
active
oldest
votes
up vote
0
down vote
GLib does now use FUTEX_WAIT_PRIVATE, since March 2015. See this commit and the related bug report.
answered Nov 22 at 17:06
Philip Withnall
2,081819
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f28896109%2fwhy-doesnt-glib-use-private-futexes%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
0
down vote
GLib does now use FUTEX_WAIT_PRIVATE, since March 2015. See this commit and the related bug report.
answered Nov 22 at 17:06
Philip Withnall
2,081819
add a comment |
up vote
0
down vote
GLib does now use FUTEX_WAIT_PRIVATE, since March 2015. See this commit and the related bug report.
answered Nov 22 at 17:06
Philip Withnall
2,081819
add a comment |
up vote
0
down vote
up vote
0
down vote
GLib does now use FUTEX_WAIT_PRIVATE, since March 2015. See this commit and the related bug report.
answered Nov 22 at 17:06
Philip Withnall
2,081819
GLib does now use FUTEX_WAIT_PRIVATE, since March 2015. See this commit and the related bug report.
answered Nov 22 at 17:06
Philip Withnall
2,081819
answered Nov 22 at 17:06
Philip Withnall
2,081819
answered Nov 22 at 17:06
Philip Withnall
2,081819
answered Nov 22 at 17:06
Philip Withnall
2,081819
2,081819
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f28896109%2fwhy-doesnt-glib-use-private-futexes%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Perhaps bug glibc mailing list re: lwn.net/Articles/229668 ? I imagine it was already discussed....
– Dima Tisnek
Feb 8 '16 at 9:54