Re: [PATCH for-8.1] tcg: Use HAVE_CMPXCHG128 instead of CONFIG_CMPXCHG128

[Thomas Huth <thuth@redhat.com>]

On 13/07/2023 22.23, Richard Henderson wrote:
> We adjust CONFIG_ATOMIC128 and CONFIG_CMPXCHG128 with
> CONFIG_ATOMIC128_OPT in atomic128.h.  It is difficult
> to tell when those changes have been applied with the
> ifdef we must use with CONFIG_CMPXCHG128.  So instead
> use HAVE_CMPXCHG128, which triggers -Werror-undef when
> the proper header has not been included.
> 
> Improves tcg_gen_atomic_cmpxchg_i128 for s390x host, which
> requires CONFIG_ATOMIC128_OPT.  Without this we fall back
> to EXCP_ATOMIC to single-step 128-bit atomics, which is
> slow enough to cause some tests to time out.
> 
> Reported-by: Thomas Huth <thuth@redhat.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> 
> Thomas, this issue does not quite match the one you bisected, but
> other than the cmpxchg, I don't see any see any qemu_{ld,st}_i128
> being used in BootLinuxS390X.test_s390_ccw_virtio_tcg.
> 
> As far as I can see, this wasn't broken by the addition of
> CONFIG_ATOMIC128_OPT, rather that fix didn't go far enough.
> 
> Anyway, test_s390_ccw_virtio_tcg now passes in 159s on our host.

Thanks, I can confirm that this fixes the issue for me, too.

Tested-by: Thomas Huth <thuth@redhat.com>