netdev - RE: sha512: make it work, undo percpu message schedule

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Date:	Fri, 13 Jan 2012 13:35:24 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Alexey Dobriyan <adobriyan@...il.com>,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	ken@...elabs.ch, Steffen Klassert <steffen.klassert@...unet.com>
Subject: RE: sha512: make it work, undo percpu message schedule

Le vendredi 13 janvier 2012 à 11:45 +0000, David Laight a écrit :
> > Trying a dynamic memory allocation, and fallback on a single
> > pre-allocated bloc of memory, shared by all cpus, protected by a
> > spinlock
> ...
> > -
> > +	static u64 msg_schedule[80];
> > +	static DEFINE_SPINLOCK(msg_schedule_lock);
> >  	int i;
> > -	u64 *W = get_cpu_var(msg_schedule);
> > +	u64 *W = kzalloc(sizeof(msg_schedule), GFP_ATOMIC |
> __GFP_NOWARN);
> >  
> > +	
> > +	if (!W) {
> > +		spin_lock_bh(&msg_schedule_lock);
> > +		W = msg_schedule;
> > +	}
> 
> If this code can be called from an ISR is the kmalloc()
> call safe?
> 

Yes, obviously, kmalloc() is IRQ safe.

> If the above is safe, wouldn't it be better to:
> 1) try to use the static buffer
> 2) try to kalloc() a buffer
> 3) spinwait for the static buffer to be free
> 

No idea of what you mean, and why you think its better.

kmalloc() propably can give us a block already hot in cpu cache.



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