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From: Brian Norris <briannorris@chromium.org>
To: "Jonas Dreßler" <verdre@v0yd.nl>
Cc: "Amitkumar Karwar" <amitkarwar@gmail.com>,
	"Ganapathi Bhat" <ganapathi017@gmail.com>,
	"Xinming Hu" <huxinming820@gmail.com>,
	"Kalle Valo" <kvalo@codeaurora.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Tsuchiya Yuto" <kitakar@gmail.com>,
	"Linux Wireless" <linux-wireless@vger.kernel.org>,
	"open list:NETWORKING DRIVERS" <netdev@vger.kernel.org>,
	"Linux Kernel" <linux-kernel@vger.kernel.org>,
	"Linux PCI" <linux-pci@vger.kernel.org>,
	"Maximilian Luz" <luzmaximilian@gmail.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Pali Rohár" <pali@kernel.org>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Johannes Berg" <johannes@sipsolutions.net>,
	"# 9798ac6d32c1 mfd : cros_ec : Add cros_ec_cmd_xfer_status
	helper" <stable@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] mwifiex: Try waking the firmware until we get an interrupt
Date: Mon, 4 Oct 2021 10:52:11 -0700	[thread overview]
Message-ID: <CAOFLbXbK5LmZbLcEs5e-0twoSkxkyKy8S6ZJVsz9Ap_a_iGZPA@mail.gmail.com> (raw)
In-Reply-To: <5f0b52be-8b9c-b015-6c5a-f2f470e37058@v0yd.nl>

Hi,

On Sun, Oct 3, 2021 at 2:18 AM Jonas Dreßler <verdre@v0yd.nl> wrote:
> So I think I have another solution that might be a lot more elegant, how
> about this:
>
> try_again:
>         n_tries++;
>
>         mwifiex_write_reg(adapter, reg->fw_status, FIRMWARE_READY_PCIE);
>
>         if (wait_event_interruptible_timeout(adapter->card_wakeup_wait_q,
>                                              READ_ONCE(adapter->int_status) != 0,
>                                              WAKEUP_TRY_AGAIN_TIMEOUT) == 0 &&
>             n_tries < MAX_N_WAKEUP_TRIES) {
>                 goto try_again;
>         }

Isn't wait_event_interruptible_timeout()'s timeout in jiffies, which
is not necessarily that predictable, and also a lot more
coarse-grained than we want? (As in, if HZ=100, we're looking at
precision on the order of 10ms, whereas the expected wakeup latency is
~6ms.) That would be OK for well-behaved PCI cases, where we never
miss a write, but it could ~double your latency for your bad systems
that will need more than one run of the loop.

Also, feels like a do/while could be cleaner, but that's a lesser detail.

> and then call wake_up_interruptible() in the mwifiex_interrupt_status()
> interrupt handler.
>
> This solution should make sure we always keep wakeup latency to a minimum
> and can still retry the register write if things didn't work.

Brian

  reply	other threads:[~2021-10-04 17:52 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 11:48 [PATCH v2 0/2] mwifiex: Work around firmware bugs on 88W8897 chip Jonas Dreßler
2021-09-14 11:48 ` [PATCH v2 1/2] mwifiex: Use non-posted PCI write when setting TX ring write pointer Jonas Dreßler
2021-09-22 11:17   ` Andy Shevchenko
2021-09-22 12:08     ` Jonas Dreßler
2021-09-22 13:22       ` Andy Shevchenko
2021-09-22 14:03   ` David Laight
2021-09-22 14:27     ` Pali Rohár
2021-09-22 15:54       ` David Laight
2021-09-30 14:27         ` Jonas Dreßler
2021-10-06 16:01           ` Jonas Dreßler
2021-09-14 11:48 ` [PATCH v2 2/2] mwifiex: Try waking the firmware until we get an interrupt Jonas Dreßler
2021-09-22 11:19   ` Andy Shevchenko
2021-09-30 18:04     ` Jonas Dreßler
2021-09-30 20:58       ` Andy Shevchenko
2021-09-30 21:07         ` Jonas Dreßler
2021-09-30 21:16           ` Andy Shevchenko
2021-10-03  9:18   ` Jonas Dreßler
2021-10-04 17:52     ` Brian Norris [this message]
2021-09-27 20:30 ` [PATCH v2 0/2] mwifiex: Work around firmware bugs on 88W8897 chip Brian Norris

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