Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1503250
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk() |
| Date | 2016-10-18 19:40 +0200 |
| Message-ID | <stGwN-4WW-23@gated-at.bofh.it> (permalink) |
| References | <stGdr-4O9-19@gated-at.bofh.it> <stGds-4O9-33@gated-at.bofh.it> <stGn7-4Sx-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tue, Oct 18, 2016 at 01:19:51PM -0400, Steven Rostedt wrote:
>
> hehe, I have the exact same patch for my -rt work.
> > +static int early_printk_cpu = -1;
> > +
> > static int early_vprintk(const char *fmt, va_list args)
> > {
> > + int n, cpu, old;
> > char buf[512];
> > +
> > + cpu = get_cpu();
> > + for (;;) {
> > + old = cmpxchg(&early_printk_cpu, -1, cpu);
> > + if (old == -1 || old == cpu)
> > + break;
Looking at this again, we really should not spin using cmpxchg(), that
thrashes the cacheline.
The below is slightly better spinning... then again, this isn't
performance code.
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -376,10 +376,16 @@ static int early_vprintk(const char *fmt
cpu = get_cpu();
for (;;) {
- old = cmpxchg(&early_printk_cpu, -1, cpu);
- if (old == -1 || old == cpu)
+ old = READ_ONCE(early_printk_cpu);
+ if (old == cpu)
break;
+ if (old == -1) {
+ old = cmpxchg(&early_printk_cpu, -1, cpu);
+ if (old == -1 || old == cpu)
+ break;
+ }
+
cpu_relax();
}
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[PATCH 0/3] make printk work again Peter Zijlstra <peterz@infradead.org> - 2016-10-18 19:20 +0200
[PATCH 1/3] printk: Fix kdb_trap_printk placement Peter Zijlstra <peterz@infradead.org> - 2016-10-18 19:20 +0200
Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement Petr Mladek <pmladek@suse.com> - 2016-10-19 16:50 +0200
Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement Peter Zijlstra <peterz@infradead.org> - 2016-10-19 17:20 +0200
Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-10-20 15:10 +0200
[PATCH 3/3] early_printk: Add simple serialization to early_vprintk() Peter Zijlstra <peterz@infradead.org> - 2016-10-18 19:20 +0200
Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk() Steven Rostedt <rostedt@goodmis.org> - 2016-10-18 19:30 +0200
Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk() Peter Zijlstra <peterz@infradead.org> - 2016-10-18 19:40 +0200
Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk() Steven Rostedt <rostedt@goodmis.org> - 2016-10-18 20:00 +0200
[PATCH 2/3] early_printk: Add force_early_printk kernel parameter Peter Zijlstra <peterz@infradead.org> - 2016-10-18 19:20 +0200
Re: [PATCH 0/3] make printk work again Peter Zijlstra <peterz@infradead.org> - 2016-10-19 16:30 +0200
Re: [PATCH 0/3] make printk work again Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-10-19 16:30 +0200
Re: [PATCH 0/3] make printk work again Jan Kara <jack@suse.cz> - 2016-10-19 17:00 +0200
Re: [PATCH 0/3] make printk work again Peter Zijlstra <peterz@infradead.org> - 2016-10-19 18:20 +0200
csiph-web