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(p200300ea8f006a0051b7bf4f06047d3d.dip0.t-ipconnect.de. [2003:ea:8f00:6a00:51b7:bf4f:604:7d3d]) by smtp.googlemail.com with ESMTPSA id p12sm9093760edr.18.2020.10.11.06.42.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 11 Oct 2020 06:42:28 -0700 (PDT) Subject: Re: [PATCH] net: stmmac: Don't call _irqoff() with hardirqs enabled To: Jakub Kicinski Cc: John Keeping , netdev@vger.kernel.org, Giuseppe Cavallaro , Alexandre Torgue , Jose Abreu , "David S. Miller" , Maxime Coquelin , linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Eric Dumazet 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> <20201010082248.22cc7656@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Heiner Kallweit Message-ID: <04d10b06-ca1c-3bfa-0a5f-730a9c8a2744@gmail.com> Date: Sun, 11 Oct 2020 15:42:24 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: <20201010082248.22cc7656@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 10.10.2020 17:22, Jakub Kicinski wrote: > 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. > Typically forced irq threading will not be enabled, therefore going back to use napi_schedule() in drivers in most cases will cause losing the benefit of the irqoff version. Something like the following should be better. Only small drawback I see is that in case of forced irq threading hrtimers will still run in hardirq context and we lose the benefit of the irqoff version in napi_watchdog(). diff --git a/net/core/dev.c b/net/core/dev.c index a146bac84..7d18560b2 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6393,7 +6393,11 @@ EXPORT_SYMBOL(napi_schedule_prep); */ void __napi_schedule_irqoff(struct napi_struct *n) { - ____napi_schedule(this_cpu_ptr(&softnet_data), n); + /* hard irqs may not be masked in case of forced irq threading */ + if (force_irqthreads) + __napi_schedule(n); + else + ____napi_schedule(this_cpu_ptr(&softnet_data), n); } EXPORT_SYMBOL(__napi_schedule_irqoff); -- 2.28.0