From: Ingo Molnar <mingo@elte.hu>
To: Jason Baron <jbaron@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Paul Mackerras <paulus@samba.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Steven Rostedt <rostedt@goodmis.org>,
a.p.zijlstra@chello.nl, davem@davemloft.net,
ddaney.cavm@gmail.com, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs
Date: Fri, 24 Feb 2012 10:08:11 +0100 [thread overview]
Message-ID: <20120224090811.GB814@elte.hu> (raw)
In-Reply-To: <20120224022512.GA3777@redhat.com>
* Jason Baron <jbaron@redhat.com> wrote:
> On Thu, Feb 23, 2012 at 06:18:42PM -0500, Mathieu Desnoyers wrote:
> > * Ingo Molnar (mingo@elte.hu) wrote:
> > >
> > > * Ingo Molnar <mingo@elte.hu> wrote:
> > >
> > > > So, a modified scheme would be:
> > > >
> > > > #include <linux/static_key.h>
> > > >
> > > > struct static_key key = STATIC_KEY_INIT_TRUE;
> > > >
> > > > if (static_key_false(&key))
> > > > do unlikely code
> > > > else
> > > > do likely code
> > > >
> > > > Or:
> > > >
> > > > if (static_key_true(&key))
> > > > do likely code
> > > > else
> > > > do unlikely code
> > > >
> > > > The static key is modified via:
> > > >
> > > > static_key_slow_inc(&key);
> > > > ...
> > > > static_key_slow_dec(&key);
> > > >
> > > > Is that API fine? I'll rework the series to such an effect if
> > > > everyone agrees.
> > >
> > > I.e. something like the patch below on top of
> > > tip:perf/jump-labels.
> > >
> > > Untested - will test it and will refactor the series if
> > > everyone's happy.
> >
> > Hi Ingo,
> >
> > Reading your documentation updates makes me realise that adding the
> > "inline" keyword in there would make the whole thing even clearer:
> >
> > struct static_key key = STATIC_KEY_INLINE_TRUE_INIT;
> > struct static_key key = STATIC_KEY_INLINE_FALSE_INIT;
> >
> > static_key_inline_true() / static_key_inline_false()
> >
> > to show that the "true/false" in there does not mean that the key will
> > always be true or false (the key value can indeed by changed by calling
> > static_key_slow_inc/dec), but that the inlined path is either the true
> > of false branch.
> >
>
> Also, as part of the API, there is a test to check the branch
> direction - which was 'jump_label_true(key)', but is now also
> 'static_key_true(key)', [...]
Yeah, there is such an overlap - I've renamed it to
static_key_enabled(), which makes sense anyway as the original
was jump_label_enabled()..
Btw., shouldnt it be an inline function? Currently it's:
bool static_key_enabled(struct static_key *key)
{
return (atomic_read(&key->enabled) > 0);
}
which is the perfect candidate for inlining. The difference to
static_key_true() is the lack of the jump label patching and the
lack of an unlikely() hint.
> [...] so we are going to have to change either the branch site
> or the test for true/false name. The above
> 'static_key_inline_true/false' solves that.
It's generally good practice to make the mostly commonly used
method names the simplest/shortest names - i.e. I don't think we
should make it longer via adding an _inline to every use.
In that sense static_key_true() has pretty optimal length - we'd
like these tests to also be visually unintrusive.
So in the latest patch (still under testing, will push it out
soon) we have:
static_key_true()
static_key_false()
static_key_enabled()
> Also, I do like having a consistent 'static_key_*' prefix for
> the entire API - definitely an improvement for me.
Yeah.
Thanks,
Ingo
next prev parent reply other threads:[~2012-02-24 9:08 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-21 20:02 [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs Jason Baron
2012-02-21 20:02 ` [PATCH 01/10] jump label: Add a WARN() if jump label key count goes negative Jason Baron
2012-02-29 10:13 ` [tip:perf/core] " tip-bot for Jason Baron
2012-02-21 20:02 ` [PATCH 02/10] jump label: fix compiler warning Jason Baron
2012-02-29 10:14 ` [tip:perf/core] jump label: Fix " tip-bot for Jason Baron
2012-02-21 20:03 ` [PATCH 03/10] jump label: introduce very_unlikely() Jason Baron
2012-02-21 20:03 ` [PATCH 04/10] jump label: introduce very_likely() Jason Baron
2012-02-21 20:03 ` [PATCH 05/10] perf: update to use 'very_unlikely()' Jason Baron
2012-02-21 20:03 ` [PATCH 06/10] tracepoints: update to use very_unlikely() Jason Baron
2012-02-21 20:03 ` [PATCH 07/10] sched: update to use very_[un]likely() Jason Baron
2012-02-21 20:03 ` [PATCH 08/10] kvm: update to use very_unlikely() Jason Baron
2012-02-21 20:03 ` [PATCH 09/10] net: " Jason Baron
2012-02-21 20:03 ` [PATCH 10/10] jump label: Add docs better explaining the whole jump label mechanism Jason Baron
2012-02-29 10:15 ` [tip:perf/core] static keys: Add docs better explaining the whole 'struct static_key' mechanism tip-bot for Jason Baron
2012-02-21 20:09 ` [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs H. Peter Anvin
2012-02-21 20:20 ` Jason Baron
2012-02-21 20:39 ` Steven Rostedt
2012-02-21 21:10 ` H. Peter Anvin
2012-02-21 21:16 ` Mathieu Desnoyers
2012-02-21 21:11 ` Mathieu Desnoyers
2012-02-22 7:32 ` Ingo Molnar
2012-02-22 7:53 ` Ingo Molnar
2012-02-22 8:01 ` H. Peter Anvin
2012-02-22 8:18 ` Ingo Molnar
2012-02-22 8:58 ` [PATCH] static keys: Introduce 'struct static_key', very_[un]likely(), static_key_slow_[inc|dec]() Ingo Molnar
2012-02-29 10:16 ` [tip:perf/core] static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]() tip-bot for Ingo Molnar
2012-02-22 9:03 ` [PATCH] jump labels: Explain the .config option better Ingo Molnar
2012-02-22 15:08 ` [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs H. Peter Anvin
2012-02-22 15:51 ` Ingo Molnar
2012-02-22 21:33 ` Paul Mackerras
2012-02-23 10:02 ` Ingo Molnar
2012-02-23 16:21 ` Jason Baron
2012-02-23 17:10 ` H. Peter Anvin
2012-02-24 9:11 ` Ingo Molnar
2012-02-23 17:18 ` Linus Torvalds
2012-02-23 22:33 ` Ingo Molnar
2012-02-23 22:39 ` Ingo Molnar
2012-02-23 22:44 ` Steven Rostedt
2012-02-23 23:18 ` Mathieu Desnoyers
2012-02-24 2:25 ` Jason Baron
2012-02-24 9:08 ` Ingo Molnar [this message]
2012-02-24 15:35 ` Jason Baron
2012-02-27 7:40 ` Ingo Molnar
2012-02-24 15:51 ` Mathieu Desnoyers
2012-02-24 16:06 ` Steven Rostedt
2012-02-24 7:52 ` static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]() Ingo Molnar
2012-02-24 7:59 ` [PATCH] " Ingo Molnar
2012-02-24 7:54 ` [PATCH] static keys: Add docs better explaining the whole 'struct static_key' mechanism Ingo Molnar
2012-02-23 22:45 ` [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs Linus Torvalds
2012-02-24 8:04 ` Ingo Molnar
2012-02-24 2:42 ` Jason Baron
2012-02-21 20:21 ` Steven Rostedt
2012-02-21 21:11 ` H. Peter Anvin
2012-02-22 6:50 ` Ingo Molnar
2012-02-22 7:03 ` H. Peter Anvin
2012-02-22 7:25 ` Ingo Molnar
2012-02-22 7:35 ` H. Peter Anvin
2012-02-22 7:48 ` Ingo Molnar
2012-02-22 7:55 ` H. Peter Anvin
2012-02-22 8:06 ` Ingo Molnar
2012-02-22 13:22 ` Steven Rostedt
2012-02-22 13:34 ` Ingo Molnar
2012-02-22 13:54 ` Steven Rostedt
2012-02-22 14:20 ` Mathieu Desnoyers
2012-02-22 14:36 ` Steven Rostedt
2012-02-22 14:56 ` Ingo Molnar
2012-02-22 15:11 ` H. Peter Anvin
2012-02-22 15:11 ` Peter Zijlstra
2012-02-22 15:47 ` Ingo Molnar
2012-02-22 15:12 ` Steven Rostedt
2012-02-22 15:15 ` H. Peter Anvin
2012-02-22 15:19 ` H. Peter Anvin
2012-02-22 15:42 ` Jason Baron
2012-02-22 15:54 ` Steven Rostedt
2012-02-22 15:56 ` Jason Baron
2012-02-22 16:08 ` Steven Rostedt
2012-02-22 15:19 ` Jason Baron
2012-02-22 15:40 ` H. Peter Anvin
2012-02-22 15:13 ` Peter Zijlstra
2012-02-22 15:32 ` Peter Zijlstra
2012-02-22 17:14 ` Richard Henderson
2012-02-22 18:28 ` H. Peter Anvin
2012-02-22 18:58 ` Jason Baron
2012-02-22 19:10 ` H. Peter Anvin
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=20120224090811.GB814@elte.hu \
--to=mingo@elte.hu \
--cc=a.p.zijlstra@chello.nl \
--cc=akpm@linux-foundation.org \
--cc=davem@davemloft.net \
--cc=ddaney.cavm@gmail.com \
--cc=hpa@zytor.com \
--cc=jbaron@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulus@samba.org \
--cc=rostedt@goodmis.org \
--cc=torvalds@linux-foundation.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 NNTP newsgroup(s).