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Sat, 17 Jul 2021 11:31:14 -0700 (PDT) Received: from [192.168.1.11] ([71.212.149.176]) by smtp.gmail.com with ESMTPSA id u3sm2511574pjn.18.2021.07.17.11.31.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 17 Jul 2021 11:31:13 -0700 (PDT) Subject: Re: [PATCH v2 01/10] accel/tcg: Reduce CF_COUNT_MASK to match TCG_MAX_INSNS To: Peter Maydell References: <20210712154004.1410832-1-richard.henderson@linaro.org> <20210712154004.1410832-2-richard.henderson@linaro.org> From: Richard Henderson Message-ID: Date: Sat, 17 Jul 2021 11:31:12 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::629; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x629.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= , Mark Cave-Ayland , QEMU Developers , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/17/21 10:30 AM, Peter Maydell wrote: > On Mon, 12 Jul 2021 at 16:42, Richard Henderson > wrote: >> >> The space reserved for CF_COUNT_MASK was overly large. >> Reduce to free up cflags bits and eliminate an extra test. >> >> Signed-off-by: Richard Henderson >> --- >> include/exec/exec-all.h | 4 +++- >> accel/tcg/translate-all.c | 5 ++--- >> 2 files changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h >> index 754f4130c9..dfe82ed19c 100644 >> --- a/include/exec/exec-all.h >> +++ b/include/exec/exec-all.h >> @@ -492,7 +492,9 @@ struct TranslationBlock { >> target_ulong cs_base; /* CS base for this block */ >> uint32_t flags; /* flags defining in which context the code was generated */ >> uint32_t cflags; /* compile flags */ >> -#define CF_COUNT_MASK 0x00007fff >> + >> +/* Note that TCG_MAX_INSNS is 512; we validate this match elsewhere. */ >> +#define CF_COUNT_MASK 0x000001ff >> #define CF_LAST_IO 0x00008000 /* Last insn may be an IO access. */ >> #define CF_MEMI_ONLY 0x00010000 /* Only instrument memory ops */ >> #define CF_USE_ICOUNT 0x00020000 >> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c >> index 4df26de858..997e44c73b 100644 >> --- a/accel/tcg/translate-all.c >> +++ b/accel/tcg/translate-all.c >> @@ -1430,9 +1430,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu, >> if (max_insns == 0) { >> max_insns = CF_COUNT_MASK; >> } >> - if (max_insns > TCG_MAX_INSNS) { >> - max_insns = TCG_MAX_INSNS; >> - } >> + QEMU_BUILD_BUG_ON(CF_COUNT_MASK + 1 != TCG_MAX_INSNS); >> + > > Previously we would allow max_insns = TCG_MAX_INSNS (512). > Now we only allow it to be 511... Hmm. Well, 0 is supposed to map to "max", currently written as max_insns = cflags & CF_COUNT_MASK; if (max_insns == 0) { max_insns = CF_COUNT_MASK; } I could just as easily map 0 -> TCG_MAX_INSNS instead. r~