linux-kernel - Re: [PATCH 4/6] bpf: hash: convert per-hashtable lock into per-bucket bit spinlock

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Message-ID: <20151218062043.GB59584@ast-mbp.thefacebook.com>
Date:	Thu, 17 Dec 2015 22:20:44 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Yang Shi <shy828301@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 4/6] bpf: hash: convert per-hashtable lock into
 per-bucket bit spinlock

On Wed, Dec 16, 2015 at 02:58:08PM +0800, Ming Lei wrote:
> On Wed, Dec 16, 2015 at 1:01 PM, Yang Shi <shy828301@...il.com> wrote:
> 
> >
> > I recalled Steven confirmed raw_spin_lock has the lockdep benefit too in the
> > patch review for changing to raw lock.
> >
> > Please check this thread out
> >  http://lists.openwall.net/netdev/2015/10/31/7
> 
> OK, looks I was wrong about the lockdep benifit, :-(
> 
> But for this lock, I think lockdep isn't such important, because it is the
> intermost lock, and it can be used just for protecting the bucket list
> and nothing else need to be covered.

I still think that overhead of normal spinlock per bucket is acceptable.
Makes the whole thing much easier to read.

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