From: Miklos Szeredi <[email protected]>
Date: Wed, 06 Jun 2007 07:26:52 +0200
> > Holding a global mutex over recvmsg() calls under AF_UNIX is pretty
> > much a non-starter, this will kill performance for multi-threaded
> > apps.
>
> That's an rwsem held for read. It's held for write in unix_gc() only
> for a short duration, and unix_gc() should only rarely be called. So
> I don't think there's any performance problem here.
It pulls a non-local cacheline into the local thread, that's extremely
expensive on SMP.
If everyone starts grabbing this thing during recvmsg() it's going to
become a really hot lock and kill performance, even if it's a read
side lock being taken.
That's why I said we need to investigate solutions involving
u->readlock, that already has to be taken and is local to the socket.
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