linux-kernel - Re: [patch V2 46/46] irqchip: Add IMS (Interrupt Message Storm) driver

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Message-ID: <20200831144522.GB1152540@nvidia.com>
Date:   Mon, 31 Aug 2020 11:45:22 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        <iommu@...ts.linux-foundation.org>, <linux-hyperv@...r.kernel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "Jon Derrick" <jonathan.derrick@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Wei Liu <wei.liu@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <rja@....com>, <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        <xen-devel@...ts.xenproject.org>, Juergen Gross <jgross@...e.com>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Megha Dey" <megha.dey@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Baolu Lu <baolu.lu@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch V2 46/46] irqchip: Add IMS (Interrupt Message Storm)
 driver - NOT FOR MERGING

On Wed, Aug 26, 2020 at 01:17:14PM +0200, Thomas Gleixner wrote:
> + * ims_queue_info - Information to create an IMS queue domain
> + * @queue_lock:		Callback which informs the device driver that
> + *			an interrupt management operation starts.
> + * @queue_sync_unlock:	Callback which informs the device driver that an
> + *			interrupt management operation ends.
> +
> + * @queue_get_shadow:   Callback to retrieve te shadow storage for a MSI
> + *			entry associated to a queue. The queue is
> + *			identified by the device struct which is used for
> + *			allocating interrupts and the msi entry index.
> + *
> + * @queue_lock() and @queue_sync_unlock() are only called for management
> + * operations on a particular interrupt: request, free, enable, disable,
> + * affinity setting.  These functions are never called from atomic context,
> + * like low level interrupt handling code. The purpose of these functions
> + * is to signal the device driver the start and end of an operation which
> + * affects the IMS queue shadow state. @queue_lock() allows the driver to
> + * do preperatory work, e.g. locking. Note, that @queue_lock() has to
> + * preserve the sleepable state on return. That means the driver cannot
> + * disable preemption and (soft)interrupts in @queue_lock and then undo
> + * that operation in @queue_sync_unlock() which restricts the lock types
> + * for eventual serialization of these operations to sleepable locks. Of
> + * course the driver can disable preemption and (soft)interrupts
> + * temporarily for internal work.
> + *
> + * On @queue_sync_unlock() the driver has to check whether the shadow state
> + * changed and issue a command to update the hardware state and wait for
> + * the command to complete. If the command fails or times out then the
> + * driver has to take care of the resulting mess as this is called from
> + * functions which have no return value and none of the callers can deal
> + * with the failure. The lock which is used by the driver to protect a
> + * operation sequence must obviously not be released before the command
> + * completes or fails. Otherwise new operations on the same interrupt line
> + * could take place and change the shadow state before the driver was able
> + * to compose the command.

I haven't looked through everything in detail, but this does look like
it is good for the mlx5 devices. Looked like it was only one small
update to the set_affinity, so not very disruptive?

Thanks,
Jason