linux-kernel - RE: [PATCH V4 05/11] vfio/pci: Use xarray for interrupt context storage

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Message-ID: <BN9PR11MB5276870C3A3CBE601A68838B8C6B9@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 28 Apr 2023 06:35:29 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Chatre, Reinette" <reinette.chatre@...el.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "yishaih@...dia.com" <yishaih@...dia.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "darwi@...utronix.de" <darwi@...utronix.de>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "tom.zanussi@...ux.intel.com" <tom.zanussi@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V4 05/11] vfio/pci: Use xarray for interrupt context
 storage

> From: Chatre, Reinette <reinette.chatre@...el.com>
> Sent: Friday, April 28, 2023 1:36 AM
> 
> Interrupt context is statically allocated at the time interrupts
> are allocated. Following allocation, the context is managed by
> directly accessing the elements of the array using the vector
> as index. The storage is released when interrupts are disabled.
> 
> It is possible to dynamically allocate a single MSI-X interrupt
> after MSI-X is enabled. A dynamic storage for interrupt context
> is needed to support this. Replace the interrupt context array with an
> xarray (similar to what the core uses as store for MSI descriptors)
> that can support the dynamic expansion while maintaining the
> custom that uses the vector as index.
> 
> With a dynamic storage it is no longer required to pre-allocate
> interrupt contexts at the time the interrupts are allocated.
> MSI and MSI-X interrupt contexts are only used when interrupts are
> enabled. Their allocation can thus be delayed until interrupt enabling.
> Only enabled interrupts will have associated interrupt contexts.
> Whether an interrupt has been allocated (a Linux irq number exists
> for it) becomes the criteria for whether an interrupt can be enabled.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>

Reviewed-by: Kevin Tian <kevin.tian@...el.com>