linux-kernel - Re: Improve spinlock performance by moving work to one core

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 25 Nov 2015 14:05:53 -0500
From:	Waiman Long <waiman.long@....com>
To:	Ling Ma <ling.ma.program@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, Ling <ling.ml@...baba-inc.com>
Subject: Re: Improve spinlock performance by moving work to one core

On 11/23/2015 04:41 AM, Ling Ma wrote:
> Hi Longman,
>
> Attachments include user space application thread.c and kernel patch
> spinlock-test.patch based on kernel 4.3.0-rc4
>
> we run thread.c with kernel patch, test original and new spinlock respectively,
> perf top -G indicates thread.c cause cache_alloc_refill and
> cache_flusharray functions to spend ~25% time on original spinlock,
> after introducing new spinlock in two functions, the cost time become ~22%.
>
> The printed data  also tell us the new spinlock improves performance
> by about 15%( 93841765576 / 81036259588) on E5-2699V3
>
> Appreciate your comments.
>
>

I saw that you make the following changes in the code:

static __always_inline void queued_spin_lock(struct qspinlock *lock)
{
u32 val;
-
+repeat:
val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL);
if (likely(val == 0))
return;
- queued_spin_lock_slowpath(lock, val);
+ goto repeat;
+ //queued_spin_lock_slowpath(lock, val);
}


This effectively changes the queued spinlock into an unfair byte lock.
Without a pause to moderate the cmpxchg() call, that is especially bad
for performance. Is the performance data above refers to the unfair byte
lock versus your new spinlock?

Cheers,
Longman
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/