[Spice-devel] [SPAM] Re: QUIC Image Decompression Method takes much time

[Frediano Ziglio]

> 
> > 
> > On Mon, Jan 11, 2016 at 04:37:32PM +0530, Ritesh Prajapati wrote:
> > > Hi Christophe,
> > > 
> > >     Do you know that by adding *"-mno-unaligned-access"* flag into CFLAGS
> > >     of
> > > MakeFile will decrease time to decompress Image through QUIC method in
> > > our
> > > ARM based A20 SoC board? Does that flag will impact anything from
> > > performance perspective?
> > 
> > No I don't know if this will help or not. IF you read through this
> > thread, you'll see that this flag has been tested (server-side though),
> > and did not seem to make a difference (iirc).
> > 
> > Christophe
> > 
> 
> The A20 is a Cortex processor (A7 or at least A6) which implements unaligned
> access.
> Anton is using
> (http://lists.freedesktop.org/archives/spice-devel/2015-October/022797.html)
> an AST2150
> (http://drivers.softpedia.com/get/GRAPHICS-BOARD/ASPEED/ASPEED-AST2150-Graphics-Driver-601097-for-Server-2008-R2-64-bit.shtml)
> which is based on ARM9 which is a V5
> (http://www.arm.com/products/processors/classic/arm9).
> See also http://www.heyrick.co.uk/armwiki/Unaligned_data_access.
> 
> I'm trying to use Qemu to reproduce the issue however even using arm926
> (which is a
> v5) behave like an arm v6 (do unaligned access). I think this is a
> misemulation on Qemu
> side (I'm using https://people.debian.org/~aurel32/qemu/armel/ and Qemu from
> Fedora 22).
> According to http://www.mjmwired.net/kernel/Documentation/arm/mem_alignment I
> should
> able to get some warning but nothing happen and data readed are not following
> v5 behavior.
> 

News on Qemu. It does not support SCTLR_A (aligned check) and SCTRL_U (unaligned
access) assuming basically that SCTLR_A is 0 (disable check) and SCTLR_U is 1
(enabled unaligned access).

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0333h/Bgbciiaf.html
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0360f/BABGDHIF.html

Frediano