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From: | Richard Henderson |
Subject: | Re: [PULL 02/10] target/sparc: Use tcg_gen_lookup_and_goto_ptr in gen_goto_tb |
Date: | Wed, 28 Jun 2023 15:55:01 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 |
On 6/28/23 15:00, BALATON Zoltan wrote:
On Wed, 28 Jun 2023, Mark Cave-Ayland wrote:From: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Signed-off-by: Richard Henderson <richard.henderson@linaro.org> Message-Id: <20230628071202.230991-2-richard.henderson@linaro.org> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> --- target/sparc/translate.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/target/sparc/translate.c b/target/sparc/translate.c index bad2ec90a0..28d4cdb8b4 100644 --- a/target/sparc/translate.c +++ b/target/sparc/translate.c @@ -318,10 +318,10 @@ static void gen_goto_tb(DisasContext *s, int tb_num, tcg_gen_movi_tl(cpu_npc, npc); tcg_gen_exit_tb(s->base.tb, tb_num); } else { - /* jump to another page: currently not optimized */ + /* jump to another page: we can use an indirect jump */ tcg_gen_movi_tl(cpu_pc, pc); tcg_gen_movi_tl(cpu_npc, npc); - tcg_gen_exit_tb(NULL, 0); + tcg_gen_lookup_and_goto_ptr();Out of curiosity, did you test this is actually faster? The reason I ask is because I've tried to optimise similar case in target/ppc by using lookup_and_goto_ptr but found it was slower than without that. I think this may depend on the usage but I wonder if that could be a generic issue with lookup_and_goto_ptr or only specific for the case I've tried.
It is faster.It should be *always* faster, because returning to the main cpu loop will always do more work than merely checking to see if we already have built the required TB.
If you see slowdowns, then *probably* you are using lookup_and_goto_ptr incorrectly in some instance, such that an interrupt has gotten overly delayed. (One must always return to the main loop after anything that might re-enable interrupts. Otherwise the interrupt handler may be delayed indefinitely. This was in fact the problem with v1 of this patch set.)
r~
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