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Re: [Qemu-devel] [RfC PATCH 0/4] make display updates thread safe.

From: Mark Cave-Ayland
Subject: Re: [Qemu-devel] [RfC PATCH 0/4] make display updates thread safe.
Date: Mon, 3 Apr 2017 13:24:02 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0

On 03/04/17 13:03, Gerd Hoffmann wrote:

>   Hi,
>> I checked the branch, is bitmap_copy_and_clear_atomic correct when you
>> have partial updates?  Maybe you need to handle partial updates of the
>> first and last word?
> Should not be a problem.  We might clear some more bits, but these are
> outsize the visible area so they should cause visible corruption (and if
> the visible area changes the display code needs to do a full refresh
> anyway).

Right. Also is there a reason that
cpu_physical_memory_snapshot_and_clear_dirty() uses BITS_PER_LEVEL when
calculating the alignment used for the first/last addresses? I would
have thought you can remove the align variable and use:

    ram_addr_t first = QEMU_ALIGN_DOWN(start, TARGET_PAGE_SIZE);
    ram_addr_t last  = QEMU_ALIGN_UP(start + length, TARGET_PAGE_SIZE);

Otherwise you end up expanding the range of your last address
considerably beyond the next page alignment. And also in the main page
loop why is BITS_PER_LEVEL used? I see that several of the internal
bitmap routines appear to use BITS_PER_LONG for compressing into the
bitmap which might be more appropriate?



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