From: "Krzysztof Wilczyński" <kw@linux.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: linux-pci@vger.kernel.org, mst@redhat.com,
Bjorn Helgaas <bhelgaas@google.com>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] pciehp: fast unplug for virtual machines
Date: Fri, 12 Nov 2021 01:00:43 +0100 [thread overview]
Message-ID: <YY2uqx4LC2J5F/w9@rocinante> (raw)
In-Reply-To: <20211111090225.946381-1-kraxel@redhat.com>
Hi Gerd,
> The PCIe specification asks the OS to wait five seconds after the
> attention button has been pressed before actually un-plugging the
> device. This gives the operator the chance to cancel the operation
> by pressing the attention button again within those five seconds.
>
> For physical hardware this makes sense. Picking the wrong button
> by accident can easily happen and it can be corrected that way.
>
> For virtual hardware the benefits are questionable. Typically
> users find the five second delay annoying.
>
> This patch adds the fast_virtual_unplug module parameter to the
> pciehp driver. When enabled (which is the default) the linux
> kernel will simply skip the delay for virtual pcie ports, which
> reduces the total time for the unplug operation from 6-7 seconds
> to 1-2 seconds.
>
> Virtual pcie ports are identified by PCI ID. For now the qemu
> pcie root ports are detected, other hardware can be added easily.
Bjorn asked to correct the PCIe references, whereas I would ask you to
change "linux" to "Linux", "qemu" to "QEMU", and generally capitalise
things where and as needed throughout.
> * @request_result: result of last user request submitted to the IRQ thread
> * @requester: wait queue to wake up on completion of user request,
> * used for synchronous slot enable/disable request via sysfs
> + * @is_virtual: virtual machine pcie port.
It would be "PCIe" here too for consistency.
> + if (dev->port->vendor == PCI_VENDOR_ID_REDHAT &&
> + dev->port->device == 0x000c)
> + /* qemu pcie root port */
> + ctrl->is_virtual = true;
I would personally move the comment above the if-statement as it looks
a little awkward added like that. You could also add a little bit more
detail why this is set for QEMU and what it's needed, etc. Also, if you
don't mind, let's change it to "QEMU" in the comment for consistency.
> - schedule_delayed_work(&ctrl->button_work, 5 * HZ);
> + if (ctrl->is_virtual && fast_virtual_unplug) {
> + schedule_delayed_work(&ctrl->button_work, 1);
> + } else {
> + schedule_delayed_work(&ctrl->button_work, 5 * HZ);
> + }
The brackets are fine but technically not needed above as per the kernel
coding style.
Krzysztof
next prev parent reply other threads:[~2021-11-12 0:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 9:02 [PATCH] pciehp: fast unplug for virtual machines Gerd Hoffmann
2021-11-11 17:00 ` Michael S. Tsirkin
2021-11-12 9:56 ` Gerd Hoffmann
2021-11-12 10:09 ` Michael S. Tsirkin
2021-11-11 21:50 ` Bjorn Helgaas
2021-11-12 11:28 ` Gerd Hoffmann
2021-11-12 0:00 ` Krzysztof Wilczyński [this message]
2021-11-14 16:39 ` Lukas Wunner
2021-11-14 17:24 ` Michael S. Tsirkin
2021-11-14 18:06 ` Lukas Wunner
2021-11-14 22:37 ` Michael S. Tsirkin
2021-11-15 9:59 ` Gerd Hoffmann
2021-11-15 7:45 ` Lukas Wunner
2021-11-15 10:09 ` Gerd Hoffmann
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