From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next-2.6] net: sock_def_readable() and friends RCU
 conversion
Date: Sat, 01 May 2010 06:56:04 +0200
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To: David Miller <davem@davemloft.net>
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Le vendredi 30 avril 2010 =C3=A0 16:35 -0700, David Miller a =C3=A9crit=
 :
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Thu, 29 Apr 2010 23:01:49 +0200
>=20
> > [PATCH net-next-2.6] net: sock_def_readable() and friends RCU conve=
rsion
>=20
> So what's the difference between call_rcu() freeing this little waitq=
ueue
> struct and doing it for the entire socket?
>=20
> We'll still be doing an RCU call every socket destroy, and now we als=
o have
> a new memory allocation/free per connection.
>=20
> This has to show up in things like 'lat_connect' and friends, does it=
 not?

Difference is this structure is small, one cache line at most.

So the cost of call_rcu() on this structure, with the well known cache
miss is very much reduced.

The thing that might cost is the smp_mb(), because it translate to a
"mfence" instruction, and it appears to cost more than a a regular
"lock ..."

Unfortunatly, oprofile doesnt work anymore on my bl460c machine after
last BIOS upgrade... Oh well...