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Subject: Re: [PATCH 1/6] Free up pf flag PF_KSOFTIRQD
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Venkatesh Pallipadi <venki@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        linux-kernel@vger.kernel.org, Paul Turner <pjt@google.com>,
        Shaun Ruffell <sruffell@digium.com>,
        Yong Zhang <yong.zhang0@gmail.com>
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Date: Thu, 21 Oct 2010 16:58:41 +0200
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Le jeudi 21 octobre 2010 à 07:36 -0700, Venkatesh Pallipadi a écrit :

> Yes. I thought about static inline part. The reason I did not make
> this static inline was because ksoftirqd was declared static in
> softirq.c and this function was getting called from sched.c.
> 

I believe you can remove the 'static' for this kind of thing.

> I did not know that this_cpu_read existed though. I guess I should be
> looking at using that elsewhere in the patchset too.
> 

Sure :)

> Also, part of the overhead you see below I think is coming from
> DEBUG_PREEMPT. That would be making every smp_processor_id() call more
> expensive. No?
> 

Right, but the point is the this_cpu_read() version doesnt have this
overhead, even if DEBUG_PREEMPT is on, at least on x86.

BTW, I lied somehow, because the way this_cpu_read() is handled,
following code :

	p == this_cpu_read(ksoftirqd);

generates :

mov     %gs:offset,%rax
cmp	%rdi,%rax

not :

cmp	%gs:offset,%rdi