> On 7 Mar 2018, at 16:14, Frediano Ziglio <fzig...@redhat.com> wrote: > >> >> On Wed, Mar 07, 2018 at 03:01:43PM +0100, Christophe de Dinechin wrote: >>> Also, on an arch like ARM. the packed attribute gives the compiler the >>> opportunity to use special mis-aligned load and store instructions. So >>> it’s a good thing, isn’t it? >> >> Iirc the compiler was not doing that much magic last time the issue came up. >> >> Christophe >> > > Don't exactly agree. > Was quite confusing. There were 2 patches, one to fix ARMv7 and alignment of > 64 bit and one to fix old ARMv5. > We didn't have much test environment and the reply for testing was very > few so we didn't have much confirmations. > When I tried directly using a ARM machine the code and speed improved a lot.
Very interesting. Last time the issue of alignment came up, I did some tests for misaligned accesses on various generations of x86 and ARM. On x86, I could see no performance impact at all for any Core-i5 and i7 machine, and barely noticeable for earlier ones. For ARM, the performance impact was more serious, but much less than I anticipated. I can try to re-do the experiment if anybody is interested. My conclusion at the time, which was a surprise to me, was that alignment no longer mattered at all on x86. > Is confusing actually that the unaligned access code is generated only for > structures. > > Frediano > _______________________________________________ > Spice-devel mailing list > Spicefirstname.lastname@example.org > https://lists.freedesktop.org/mailman/listinfo/spice-devel _______________________________________________ Spice-devel mailing list Spiceemail@example.com https://lists.freedesktop.org/mailman/listinfo/spice-devel