Re: [PATCH net-next 3/4] net: dev: Makes sure netif_rx() can be invoked in any context.

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Eric Dumazet <edumazet@google.com>
Cc: bpf <bpf@vger.kernel.org>, netdev <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH net-next 3/4] net: dev: Makes sure netif_rx() can be invoked in any context.
Date: Thu, 3 Feb 2022 18:45:22 +0100	[thread overview]
Message-ID: <YfwUskgPuOREd9hs@linutronix.de> (raw)
In-Reply-To: <YfwGcHv6XQytcq68@linutronix.de>

On 2022-02-03 17:44:33 [+0100], To Eric Dumazet wrote:
> > I guess the cost of the  local_bh_enable()/local_bh_disable() pair
> > will be roughly the same, please measure it :)
> 
> We would avoid that branch maybe that helps. Will measure.

|  BH OFF/ON     : 722922586
|  BH OFF/ON     : 722931661
|  BH OFF/ON     : 725341486
|  BH OFF/ON     : 725909591
|  BH OFF/ON     : 741705606
|  BH OFF/ON-OPT : 536683873
|  BH OFF/ON-OPT : 536933779
|  BH OFF/ON-OPT : 536967581
|  BH OFF/ON-OPT : 537109700
|  BH OFF/ON-OPT : 537148631

in a tight loop of 100000000 iterations:
BH OFF/ON = local_bh_disable(); local_bh_enable()
BH OFF/ON-OPT = local_bh_disable(); local_bh_enable_opt()
where local_bh_enable_opt() is the proposed function.

725341486 = ~7.3ns for one iteration.
536967581 = ~5.4ns for one iteration.

This is without tracing+lockdep. So I don't need to sell this to peterz
and focus one the previously suggested version.

Sebastian