netdev - Re: [PATCH v4 2/9] bgmac: leave interrupts disabled as long as there is work to do

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Message-ID: <CACna6rzASVB-j8TxDzybC5FC+BhJFA-3e9LGTXqfP8FgSnH0bA@mail.gmail.com>
Date:	Mon, 13 Apr 2015 17:06:13 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Felix Fietkau <nbd@...nwrt.org>
Cc:	Network Development <netdev@...r.kernel.org>,
	Hauke Mehrtens <hauke@...ke-m.de>
Subject: Re: [PATCH v4 2/9] bgmac: leave interrupts disabled as long as there
 is work to do

On 13 April 2015 at 17:03, Felix Fietkau <nbd@...nwrt.org> wrote:
> On 2015-04-13 16:34, Rafał Miłecki wrote:
>> On 13 April 2015 at 15:52, Felix Fietkau <nbd@...nwrt.org> wrote:
>>> Always poll rx and tx during NAPI poll instead of relying on the status
>>> of the first interrupt. This prevents bgmac_poll from leaving unfinished
>>> work around until the next IRQ.
>>> In my tests this makes bridging/routing throughput under heavy load more
>>> stable and ensures that no new IRQs arrive as long as bgmac_poll uses up
>>> the entire budget.
>>
>> What do you think about keeping u32 int_status; and just updating it
>> at the end of bgmac_poll? In case you decide to implement multiple TX
>> queues, it may be cheaper to just check a single bit in memory instead
>> reading DMA ring status.
> Events might arrive in the mean time. I ran some tests, and not checking
> the irq status for processing rx/tx gave me fewer total IRQs under load.

But you do check the status, I mean the following line:
if (bgmac_read(bgmac, BGMAC_INT_STATUS) & (BGMAC_IS_TX0 | BGMAC_IS_RX))

Would it make sense to do
bgmac->int_status = bgmac_read(bgmac, BGMAC_INT_STATUS);
if (bgmac->int_status)
instead?
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