[PATCH] lglock: add read-preference local-global rwlock

Lai Jiangshan laijs at cn.fujitsu.com
Wed Mar 6 02:54:40 EST 2013

On 03/03/13 01:06, Oleg Nesterov wrote:
> On 03/02, Michel Lespinasse wrote:
>> My version would be slower if it needs to take the
>> slow path in a reentrant way, but I'm not sure it matters either :)
> I'd say, this doesn't matter at all, simply because this can only happen
> if we race with the active writer.

It can also happen when interrupted. (still very rarely)

		__this_cpu_read() returns 0.
		arch_spin_trylock() fails
		slowpath, any nested will be slowpath too.

I saw get_online_cpu_atomic() is called very frequent.
And the above thing happens in one CPU rarely, but how often it
happens in the whole system if we have 4096 CPUs?
(I worries to much. I tend to remove FALLBACK_BASE now, we should
add it only after we proved we needed it, this part is not proved)


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