Hi Richard,
On 13/7/23 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.
IIUC:
If we have CONFIG_ATOMIC128, we use qatomic_cmpxchg__nocheck;
else if we have CONFIG_CMPXCHG128 we use __sync_val_compare_and_swap_16;
in both cases we set HAVE_CMPXCHG128;
otherwise we can not use atomic128 cmpxchg().
(I'm trying to figure why we need both CONFIGs).