Re: [PATCH v2] PCI: Fix no-op wait after secondary bus reset

From: Lukas Wunner <lukas@wunner.de>
To: Sheng Bi <windy.bi.enflame@gmail.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] PCI: Fix no-op wait after secondary bus reset
Date: Sat, 21 May 2022 14:49:10 +0200	[thread overview]
Message-ID: <20220521124910.GA13556@wunner.de> (raw)
In-Reply-To: <CAGdb+H2_pX4TzG=sJ8XE6KiyWW9niJQawCbcDN2byxDfybukiA@mail.gmail.com>

On Sat, May 21, 2022 at 04:36:10PM +0800, Sheng Bi wrote:
> If so, I also want to align the polling things mentioned in the
> question from Alex, since pci_dev_wait() is also used for reset
> functions other than SBR. To Bjorn, Alex, Lucas, how do you think if
> we need to change the polling in pci_dev_wait() to 20ms intervals, or
> keep binary exponential back-off with probable unexpected extra
> timeout delay.

The exponential backoff should probably be capped at some point
to avoid excessive wait delays.  I guess the rationale for
exponential backoff is to not poll too frequently.
Capping at 20 msec or 100 msec may be reasonable, i.e.:

-		delay *= 2;
+		delay = min(delay * 2, 100);

Thanks,

Lukas