Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sat, 10 Oct 2020 08:22:48 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Heiner Kallweit <hkallweit1@gmail.com>
Cc:     John Keeping <john@metanate.com>, netdev@vger.kernel.org,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH] net: stmmac: Don't call _irqoff() with hardirqs enabled
Message-ID: <20201010082248.22cc7656@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
In-Reply-To: <070b2b87-f38c-088d-4aaf-12045dbd92f7@gmail.com>
References: <20201008162749.860521-1-john@metanate.com>
        <8036d473-68bd-7ee7-e2e9-677ff4060bd3@gmail.com>
        <20201009085805.65f9877a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
        <725ba7ca-0818-074b-c380-15abaa5d037b@gmail.com>
        <070b2b87-f38c-088d-4aaf-12045dbd92f7@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Sat, 10 Oct 2020 15:08:15 +0200 Heiner Kallweit wrote:
> On 09.10.2020 18:06, Heiner Kallweit wrote:
> > On 09.10.2020 17:58, Jakub Kicinski wrote:  
> >> On Fri, 9 Oct 2020 16:54:06 +0200 Heiner Kallweit wrote:  
> >>> I'm thinking about a __napi_schedule version that disables hard irq's
> >>> conditionally, based on variable force_irqthreads, exported by the irq
> >>> subsystem. This would allow to behave correctly with threadirqs set,
> >>> whilst not loosing the _irqoff benefit with threadirqs unset.
> >>> Let me come up with a proposal.  
> >>
> >> I think you'd need to make napi_schedule_irqoff() behave like that,
> >> right?  Are there any uses of napi_schedule_irqoff() that are disabling
> >> irqs and not just running from an irq handler?
> >>  
> > Right, the best approach depends on the answer to the latter question.
> > I didn't check this yet, therefore I described the least intrusive approach.
> >   
> 
> With some help from coccinelle I identified the following functions that
> call napi_schedule_irqoff() or __napi_schedule_irqoff() and do not run
> from an irq handler (at least not at the first glance).
> 
> dpaa2_caam_fqdan_cb
> qede_simd_fp_handler
> mlx4_en_rx_irq
> mlx4_en_tx_irq

Don't know the others but FWIW the mlx4 ones run from an IRQ handler,
AFAICT:

static irqreturn_t mlx4_interrupt(int irq, void *dev_ptr)
static irqreturn_t mlx4_msi_x_interrupt(int irq, void *eq_ptr)
  mlx4_eq_int()
    mlx4_cq_completion
      cq->comp()

> qeth_qdio_poll
> netvsc_channel_cb
> napi_watchdog

This one runs from a hrtimer, which I believe will be a hard irq
context on anything but RT. I could be wrong.