netdev - Re: [PATCH] NET : convert IP route cache garbage colleciton from softirq processing to a workqueue

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Date:	Wed, 12 Sep 2007 12:18:30 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] NET : convert IP route cache garbage colleciton from
 softirq processing to a workqueue

On Wed, 12 Sep 2007 11:00:54 +0100
Christoph Hellwig <hch@...radead.org> wrote:

> This looks nice in general, getting things out of softirq context is
> always good.

I am preparing a patch to net/ipv4/route.c to migrate rt_check_expire()
as well.

> 
> On Tue, Sep 11, 2007 at 02:56:13PM +0200, Eric Dumazet wrote:
> >  #if RT_CACHE_DEBUG >= 2
> >  static atomic_t			 dst_total = ATOMIC_INIT(0);
> >  #endif
> > -static unsigned long dst_gc_timer_expires;
> > -static unsigned long dst_gc_timer_inc = DST_GC_MAX;
> > -static void dst_run_gc(unsigned long);
> > +static struct {
> > +	spinlock_t		lock;
> > +	struct dst_entry 	*list;
> > +	unsigned long		timer_inc;
> > +	unsigned long		timer_expires;
> > +} dst_garbage = {
> > +	.lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
> > +	.timer_inc = DST_GC_MAX,
> > +};
> 
> Can you please et rid of this useless struct?  It just complicates
> the code and means we can't use the proper DEFINE_SPINLOCK initializer.

When using the standard DEFINE_SPINLOCK initializer, the lock is in the 
data section, while list is in bss section.

This 'useless struct' makes lock/list being on the same cache line, so 
reduces latency of __dst_free(). I wish more structures in kernel be used
instead of relying on random placement of the linker...

> 
> > +DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
> 
> This should be static.

Yes I agree

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