From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755470AbeARMoO (ORCPT <rfc822;w@1wt.eu>);
        Thu, 18 Jan 2018 07:44:14 -0500
Received: from mail-wm0-f67.google.com ([74.125.82.67]:35021 "EHLO
        mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753529AbeARMoM (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 18 Jan 2018 07:44:12 -0500
X-Google-Smtp-Source: ACJfBosEHp4YocPcdsE4wkKVMAnrtpzosOvCxx4sV0MGYR5/6tMpKcB+wnOHBwA+11n0/UBgUVYr0Q==
Message-ID: <1516279448.2762.7.camel@arista.com>
Subject: Re: [RFC PATCH 0/5] softirq: Per vector threading v2
From: Dmitry Safonov <dima@arista.com>
To: Frederic Weisbecker <frederic@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Levin Alexander <alexander.levin@verizon.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Wanpeng Li <wanpeng.li@hotmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Eric Dumazet <edumazet@google.com>, Radu Rendec <rrendec@arista.com>,
        Ingo Molnar <mingo@kernel.org>,
        Stanislaw Gruszka <sgruszka@redhat.com>,
        Paolo Abeni <pabeni@redhat.com>, Rik van Riel <riel@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Miller <davem@davemloft.net>
Date: Thu, 18 Jan 2018 12:44:08 +0000
In-Reply-To: <20180118040916.GA25885@lerouge>
References: <1516077640-19718-1-git-send-email-frederic@kernel.org>
         <20180117145620.213cb5ad@vento.lan> <20180117180713.GA17735@lerouge>
         <CA+55aFzojENpf+-fEhkNL_RaQbtC0FoB6x7DDXqZCScCOAUmQg@mail.gmail.com>
         <20180118025539.GA20310@lerouge>
         <CA+55aFwzFn=gbqLmmc=R9Tv1bX1GoSWsbcTKzG=nrJZKsj9nVw@mail.gmail.com>
         <20180118040916.GA25885@lerouge>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.24.6 (3.24.6-1.fc26) 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 2018-01-18 at 05:09 +0100, Frederic Weisbecker wrote:
> On Wed, Jan 17, 2018 at 07:09:39PM -0800, Linus Torvalds wrote:
> > It should never trigger under any normal load, but I think it
> > *should*
> > trigger under the load that the networking people worry about. If
> > you
> > get a flood of UDP packets, and spend a lot of time in softirqs,
> > I'm
> > pretty sure you'd hit that case of seeing the same softirq re-
> > raised
> > fairly naturally and quickly.
> 
> Ok after a quick tracing check, it seems that executing the same
> softirq
> vector twice in the same interrupt does not happen without much
> stress.

Uhm, yes it should.. but that was what I originally saw on hw - that
raising a new softirq under UDP packet storm might happen slower than
expected. And a new softirq is raised only after the first one was
processed. Which results in rare deferring.

-- 
            Dima