linux-kernel - Re: [PATCH v2] ath10k: transmit queued frames after waking queues

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Date:   Tue, 22 May 2018 15:16:37 -0700
From:   Rajkumar Manoharan <rmanohar@...eaurora.org>
To:     Niklas Cassel <niklas.cassel@...aro.org>
Cc:     Kalle Valo <kvalo@....qualcomm.com>,
        "David S. Miller" <davem@...emloft.net>,
        ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-wireless-owner@...r.kernel.org, erik.stromdahl@...il.com
Subject: Re: [PATCH v2] ath10k: transmit queued frames after waking queues

On 2018-05-22 14:15, Niklas Cassel wrote:
> On Mon, May 21, 2018 at 04:11:38PM -0700, Rajkumar Manoharan wrote:
>> On 2018-05-21 13:43, Niklas Cassel wrote:
>> > The following problem was observed when running iperf:
[...]
>> 
>> Sorry for the late response. ath10k_mac_tx_push_pending is already 
>> called
>> at the end of NAPI handler. Isn't that enough to process pending 
>> frames?
> 
> This is true for e.g. ATH10K_BUS_PCI and ATH10K_BUS_SNOC,
> but not for e.g. ATH10K_BUS_SDIO and ATH10K_BUS_USB.
> 
> While there is some SDIO code merged in Kalle's tree already,
> this problem was found when merging
> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/?h=ath10k-pending-sdio-usb
> with Kalle's ath-next branch.
> 
>> 
>> Earlier we observed performance issues in calling push_pending from 
>> each
>> tx completion. IMHO this change may introduce the same problem again.
> 
> I prefer functional TX over performance issues,
> but I agree that it is unfortunate that SDIO doesn't use
> ath10k_htt_txrx_compl_task().
> Erik, is there a reason for this?
> 
Thanks for details. Now I see your problem. In case of low latency 
devices (PCI/SNOC/AHB),
all CE rings interrupts are serviced first and later consolidated data 
processing done
from ath10k_htt_txrx_compl_task and then ath10k_mac_tx_push_pending is 
called from NAPI Poll.

In case of high latency devices (USB/SDIO), each endpoints are serviced 
and all tx/rx jobs
are completed from the same context. Hence no need of consolidated 
processing.

> Perhaps it would be possible to call ath10k_mac_tx_push_pending()
> from the equivalent to ath10k_htt_txrx_compl_task(),
> but from SDIO's point of view.
> 
> Another solution might be to change so that we only call
> ath10k_mac_tx_push_pending() from ath10k_txrx_tx_unref()
> if (htt->num_pending_tx == 0). That should decrease the number
> of calls to ath10k_mac_tx_push_pending(), while still avoiding
> a "TX deadlock" scenario for SDIO.
> 
This issue is specific to HL devices. But your change is common which 
will impact LL devices.
I would prefer to call ath10k_mac_tx_push_pending after processing all 
received mbox/urb messages.
Export ath10k_mac_tx_push_pending API and call it from USB/SDIO irq 
handler. Any thoughts?

-Rajkumar