netdev - Re: [PATCH 1/2] rsi: Move card interrupt handling to RX thread

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Message-Id: <20201110185534.12EA1C4339C@smtp.codeaurora.org>
Date:   Tue, 10 Nov 2020 18:55:34 +0000 (UTC)
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Marek Vasut <marex@...x.de>
Cc:     linux-wireless@...r.kernel.org, Marek Vasut <marex@...x.de>,
        Angus Ainslie <angus@...ea.ca>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Martin Kepplinger <martink@...teo.de>,
        Sebastian Krzyszkowiak <sebastian.krzyszkowiak@...i.sm>,
        Siva Rebbagondla <siva8118@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] rsi: Move card interrupt handling to RX thread

Marek Vasut <marex@...x.de> wrote:

> The interrupt handling of the RS911x is particularly heavy. For each RX
> packet, the card does three SDIO transactions, one to read interrupt
> status register, one to RX buffer length, one to read the RX packet(s).
> This translates to ~330 uS per one cycle of interrupt handler. In case
> there is more incoming traffic, this will be more.
> 
> The drivers/mmc/core/sdio_irq.c has the following comment, quote "Just
> like traditional hard IRQ handlers, we expect SDIO IRQ handlers to be
> quick and to the point, so that the holding of the host lock does not
> cover too much work that doesn't require that lock to be held."
> 
> The RS911x interrupt handler does not fit that. This patch therefore
> changes it such that the entire IRQ handler is moved to the RX thread
> instead, and the interrupt handler only wakes the RX thread.
> 
> This is OK, because the interrupt handler only does things which can
> also be done in the RX thread, that is, it checks for firmware loading
> error(s), it checks buffer status, it checks whether a packet arrived
> and if so, reads out the packet and passes it to network stack.
> 
> Moreover, this change permits removal of a code which allocated an
> skbuff only to get 4-byte-aligned buffer, read up to 8kiB of data
> into the skbuff, queue this skbuff into local private queue, then in
> RX thread, this buffer is dequeued, the data in the skbuff as passed
> to the RSI driver core, and the skbuff is deallocated. All this is
> replaced by directly calling the RSI driver core with local buffer.
> 
> Signed-off-by: Marek Vasut <marex@...x.de>
> Cc: Angus Ainslie <angus@...ea.ca>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Kalle Valo <kvalo@...eaurora.org>
> Cc: Lee Jones <lee.jones@...aro.org>
> Cc: Martin Kepplinger <martink@...teo.de>
> Cc: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@...i.sm>
> Cc: Siva Rebbagondla <siva8118@...il.com>
> Cc: linux-wireless@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Tested-by: Martin Kepplinger <martin.kepplinger@...i.sm>

2 patches applied to wireless-drivers-next.git, thanks.

287431463e78 rsi: Move card interrupt handling to RX thread
abd131a19f6b rsi: Clean up loop in the interrupt handler

-- 
https://patchwork.kernel.org/project/linux-wireless/patch/20201103180941.443528-1-marex@denx.de/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches