Re: [PATCH] pciehp: fast unplug for virtual machines

Michael S. Tsirkin
2021-11-11T17:00:53Z

On Thu, Nov 11, 2021 at 10:02:24AM +0100, Gerd Hoffmann wrote:
> 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.

BTW how come it's still taking seconds, not milliseconds?

> Virtual pcie ports are identified by PCI ID. For now the qemu
> pcie root ports are detected, other hardware can be added easily.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> drivers/pci/hotplug/pciehp.h | 3 +++
> drivers/pci/hotplug/pciehp_core.c | 5 +++++
> drivers/pci/hotplug/pciehp_ctrl.c | 11 ++++++++++-
> 3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index 69fd401691be..131ffec2e947 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -79,6 +79,7 @@ extern int pciehp_poll_time;
> * @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.
> *
> * PCIe hotplug has a 1:1 relationship between controller and slot, hence
> * unlike other drivers, the two aren't represented by separate structures.
> @@ -109,6 +110,8 @@ struct controller {
> unsigned int ist_running;
> int request_result;
> wait_queue_head_t requester;
> +
> + bool is_virtual;
> };
>
> /**
> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> index ad3393930ecb..28867ec33f5b 100644
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -227,6 +227,11 @@ static int pciehp_probe(struct pcie_device *dev)
> goto err_out_shutdown_notification;
> }
>
> + if (dev->port->vendor == PCI_VENDOR_ID_REDHAT &&
> + dev->port->device == 0x000c)
> + /* qemu pcie root port */
> + ctrl->is_virtual = true;
> +
> pciehp_check_presence(ctrl);
>
> return 0;
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index 529c34808440..119bb11f87d6 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -15,12 +15,17 @@
>
> #define dev_fmt(fmt) "pciehp: " fmt
>
> +#include <linux/moduleparam.h>
> #include <linux/kernel.h>
> #include <linux/types.h>
> #include <linux/pm_runtime.h>
> #include <linux/pci.h>
> #include "pciehp.h"
>
> +static bool fast_virtual_unplug = true;
> +module_param(fast_virtual_unplug, bool, 0644);
> +MODULE_PARM_DESC(fast_virtual_unplug, "Fast unplug (don't wait 5 seconds) for virtual machines.");
> +
> /* The following routines constitute the bulk of the
> hotplug controller logic
> */
> @@ -176,7 +181,11 @@ void pciehp_handle_button_press(struct controller *ctrl)
> /* blink power indicator and turn off attention */
> pciehp_set_indicators(ctrl, PCI_EXP_SLTCTL_PWR_IND_BLINK,
> PCI_EXP_SLTCTL_ATTN_IND_OFF);
> - 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);
> + }
> break;
> case BLINKINGOFF_STATE:
> case BLINKINGON_STATE:
> --
> 2.33.1