From: Jason Gunthorpe <jgg@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Abhishek Sahu <abhsahu@nvidia.com>,
Cornelia Huck <cohuck@redhat.com>,
Yishai Hadas <yishaih@nvidia.com>,
Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
Kevin Tian <kevin.tian@intel.com>,
"Rafael J . Wysocki" <rafael@kernel.org>,
Max Gurtovoy <mgurtovoy@nvidia.com>,
Bjorn Helgaas <bhelgaas@google.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
linux-pm@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH v5 1/5] vfio: Add the device features for the low power entry and exit
Date: Tue, 2 Aug 2022 11:04:52 -0300 [thread overview]
Message-ID: <YukvBBClrbCbIitm@nvidia.com> (raw)
In-Reply-To: <20220801124253.11c24d91.alex.williamson@redhat.com>
On Mon, Aug 01, 2022 at 12:42:53PM -0600, Alex Williamson wrote:
> On Wed, 27 Jul 2022 11:37:02 +0530
> Abhishek Sahu <abhsahu@nvidia.com> wrote:
>
> > On 7/26/2022 10:53 PM, Jason Gunthorpe wrote:
> > > On Tue, Jul 26, 2022 at 06:17:18PM +0530, Abhishek Sahu wrote:
> > >> Thanks Alex for your thorough review of uAPI.
> > >> I have incorporated all the suggestions.
> > >> Following is the updated uAPI.
> > >>
> > >> /*
> > >> * Upon VFIO_DEVICE_FEATURE_SET, allow the device to be moved into a low power
> > >> * state with the platform-based power management. Device use of lower power
> > >> * states depends on factors managed by the runtime power management core,
> > >> * including system level support and coordinating support among dependent
> > >> * devices. Enabling device low power entry does not guarantee lower power
> > >> * usage by the device, nor is a mechanism provided through this feature to
> > >> * know the current power state of the device. If any device access happens
> > >> * (either from the host or through the vfio uAPI) when the device is in the
> > >> * low power state, then the host will move the device out of the low power
> > >> * state as necessary prior to the access. Once the access is completed, the
> > >> * device may re-enter the low power state. For single shot low power support
> > >> * with wake-up notification, see
> > >> * VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY_WITH_WAKEUP below. Access to mmap'd
> > >> * device regions is disabled on LOW_POWER_ENTRY and may only be resumed after
> > >> * calling LOW_POWER_EXIT.
> > >> */
> > >> #define VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY 3
> > >>
> > >> /*
> > >> * This device feature has the same behavior as
> > >> * VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY with the exception that the user
> > >> * provides an eventfd for wake-up notification.
> > >
> > > It feels like this should be one entry point instead of two.
> > >
> > > A flag "automatic re-sleep" and an optional eventfd (-1 means not
> > > provided) seems to capture both of these behaviors in a bit clearer
> > > and extendable way.
>
> I think the mutual exclusion between re-entrant mode and one-shot is
> quite a bit more subtle in the version below, so I don't particularly
> find this cleaner. Potentially we could have variant drivers support
> one w/o the other in the previously proposed model as well. It's
> interesting to see this suggestion since since we seem to have a theme
> of making features single purpose elsewhere. Thanks,
It is still quite single purpose, just
VFIO_DEVICE_LOW_POWER_REENTERY_DISABLE is some minor customization of
that single purpose.
Either the flag is set or not, it isn't subtle..
Jason
next prev parent reply other threads:[~2022-08-02 14:05 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-19 12:15 [PATCH v5 0/5] vfio/pci: power management changes Abhishek Sahu
2022-07-19 12:15 ` [PATCH v5 1/5] vfio: Add the device features for the low power entry and exit Abhishek Sahu
2022-07-21 22:34 ` Alex Williamson
2022-07-25 14:40 ` Abhishek Sahu
2022-07-25 22:09 ` Alex Williamson
2022-07-26 12:47 ` Abhishek Sahu
2022-07-26 13:13 ` Cornelia Huck
2022-07-26 14:17 ` Alex Williamson
2022-07-26 17:23 ` Jason Gunthorpe
2022-07-27 6:07 ` Abhishek Sahu
2022-08-01 18:42 ` Alex Williamson
2022-08-02 14:04 ` Jason Gunthorpe [this message]
2022-08-02 15:41 ` Alex Williamson
2022-08-02 16:35 ` Jason Gunthorpe
2022-08-02 16:57 ` Alex Williamson
2022-08-02 17:01 ` Jason Gunthorpe
2022-08-03 6:32 ` Abhishek Sahu
2022-07-19 12:15 ` [PATCH v5 2/5] vfio: Increment the runtime PM usage count during IOCTL call Abhishek Sahu
2022-07-21 22:34 ` Alex Williamson
2022-07-19 12:15 ` [PATCH v5 3/5] vfio/pci: Mask INTx during runtime suspend Abhishek Sahu
2022-07-19 12:15 ` [PATCH v5 4/5] vfio/pci: Implement VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY/EXIT Abhishek Sahu
2022-07-21 22:34 ` Alex Williamson
2022-07-25 14:48 ` Abhishek Sahu
2022-07-19 12:15 ` [PATCH v5 5/5] vfio/pci: Implement VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY_WITH_WAKEUP Abhishek Sahu
2022-07-21 22:34 ` Alex Williamson
2022-07-25 15:04 ` Abhishek Sahu
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