[Qemu-devel] [PULL for-2.5] TCG highwater fix

[Qemu-devel] [PULL for-2.5] TCG highwater fix

[Richard Henderson]

A last-minute fix for -rc2.


r~


The following changes since commit a2485925f76d01795f041fd63663d8582139fda4:

  Merge remote-tracking branch 'remotes/dgibson/tags/ppc-for-2.5-20151130' into staging (2015-11-30 17:09:35 +0000)

are available in the git repository at:

  git://github.com/rth7680/qemu.git tags/pull-tcg-20151201

for you to fetch changes up to b17a6d3390f87620735f7efb03bb1c96682ff449:

  tcg: Increase the highwater reservation (2015-12-01 14:36:32 -0800)

----------------------------------------------------------------
Last minute fix

----------------------------------------------------------------
Richard Henderson (1):
      tcg: Increase the highwater reservation

 tcg/tcg.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

[Qemu-devel] [PULL] tcg: Increase the highwater reservation

[Richard Henderson]

If there are a lot of guest memory ops in the TB, the amount of
code generated by tcg_out_tb_finalize could be well more than 1k.
In the short term, increase the reservation larger than any TB
seen in practice.

Reported-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 tcg/tcg.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tcg/tcg.c b/tcg/tcg.c
index b20ed19..a163541 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -388,7 +388,11 @@ void tcg_prologue_init(TCGContext *s)
     /* Compute a high-water mark, at which we voluntarily flush the buffer
        and start over.  The size here is arbitrary, significantly larger
        than we expect the code generation for any one opcode to require.  */
-    s->code_gen_highwater = s->code_gen_buffer + (total_size - 1024);
+    /* ??? We currently have no good estimate for, or checks in,
+       tcg_out_tb_finalize.  If there are quite a lot of guest memory ops,
+       the number of out-of-line fragments could be quite high.  In the
+       short-term, increase the highwater buffer.  */
+    s->code_gen_highwater = s->code_gen_buffer + (total_size - 64*1024);
 
     tcg_register_jit(s->code_gen_buffer, total_size);
 
-- 
2.5.0

Re: [Qemu-devel] [PULL for-2.5] TCG highwater fix

[Peter Maydell]

On 1 December 2015 at 22:40, Richard Henderson <rth@twiddle.net> wrote:
> A last-minute fix for -rc2.
>
>
> r~
>
>
> The following changes since commit a2485925f76d01795f041fd63663d8582139fda4:
>
>   Merge remote-tracking branch 'remotes/dgibson/tags/ppc-for-2.5-20151130' into staging (2015-11-30 17:09:35 +0000)
>
> are available in the git repository at:
>
>   git://github.com/rth7680/qemu.git tags/pull-tcg-20151201
>
> for you to fetch changes up to b17a6d3390f87620735f7efb03bb1c96682ff449:
>
>   tcg: Increase the highwater reservation (2015-12-01 14:36:32 -0800)
>
> ----------------------------------------------------------------
> Last minute fix
>
> ----------------------------------------------------------------
> Richard Henderson (1):
>       tcg: Increase the highwater reservation
>
>  tcg/tcg.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

Applied, thanks.

-- PMM