linux-kernel - Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping

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Message-ID: <20210810155058.4199a86b.alex.williamson@redhat.com>
Date:   Tue, 10 Aug 2021 15:50:58 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, peterx@...hat.com
Subject: Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping_range()

On Tue, 10 Aug 2021 13:55:00 +0100
Christoph Hellwig <hch@...radead.org> wrote:

> On Tue, Aug 10, 2021 at 08:57:22AM -0300, Jason Gunthorpe wrote:
> > I'm not sure there is a real performance win to chase here? Doesn't
> > this only protect mmap against reset? The mmap isn't performance
> > sensitive, right?
> > 
> > If this really needs extra optimization adding a rwsem to the devset
> > and using that across the whole set would surely be sufficient.  
> 
> Every mmio read or write takes memory_lock.

Exactly.  Ideally we're not using that path often, but I don't think
that's a good excuse to introduce memory access serialization, or even
dependencies between devices.  Thanks,

Alex