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Jones" , LIU Zhiwei Cc: qemu-devel@nongnu.org, qemu-riscv@nongnu.org, palmer@dabbelt.com, alistair.francis@wdc.com, bin.meng@windriver.com, liweiwei@iscas.ac.cn, dbarboza@ventanamicro.com, pbonzini@redhat.com References: <20231008215147.3362612-1-rjones@redhat.com> <20231008215147.3362612-2-rjones@redhat.com> <50894b0f-effe-4e0d-81a9-51dc24a05489@linux.alibaba.com> <20231009125321.GR7636@redhat.com> From: LIU Zhiwei In-Reply-To: <20231009125321.GR7636@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::636; envelope-from=baxiantai@gmail.com; helo=mail-pl1-x636.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, FREEMAIL_FROM=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 2023/10/9 20:53, Richard W.M. Jones wrote: > On Mon, Oct 09, 2023 at 08:36:28PM +0800, LIU Zhiwei wrote: >> On 2023/10/9 5:50, Richard W.M. Jones wrote: >>> RISCV_CPU(cs) uses a checked cast. When QOM cast debugging is enabled >>> this adds about 5% total overhead when emulating RV64 on x86-64 host. >>> >>> Using a RISC-V guest with 16 vCPUs, 16 GB of guest RAM, virtio-blk >>> disk. The guest has a copy of the qemu source tree. The test >>> involves compiling the qemu source tree with 'make clean; time make -j16'. >>> >>> Before making this change the compile step took 449 & 447 seconds over >>> two consecutive runs. >>> >>> After making this change, 428 & 422 seconds. >>> >>> The saving is about 5%. >>> >>> Thanks: Paolo Bonzini >>> Signed-off-by: Richard W.M. Jones >>> Reviewed-by: Daniel Henrique Barboza >>> --- >>> target/riscv/cpu_helper.c | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c >>> index 3a02079290..479d9863ae 100644 >>> --- a/target/riscv/cpu_helper.c >>> +++ b/target/riscv/cpu_helper.c >>> @@ -66,7 +66,11 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc, >>> uint64_t *cs_base, uint32_t *pflags) >>> { >>> CPUState *cs = env_cpu(env); >>> - RISCVCPU *cpu = RISCV_CPU(cs); >>> + /* >>> + * Using the checked cast RISCV_CPU(cs) imposes ~ 5% overhead when >>> + * QOM cast debugging is enabled, so use a direct cast instead. >>> + */ >>> + RISCVCPU *cpu = (RISCVCPU *)cs; >> This function is very hot. Maybe we should cache the tbflags instead >> of calculate it here. Otherwise, > This function is indeed very hot, taking over 20% of total host time > in my guest stress test. > > How would we cache the flags? AIUI they simply depend on machine > state and we must recalculate them either when the machine state > changes (sprinkle "update_tbflags" everywhere) Yes, we should do in this way. > or here. If you have > any suggestions I can try things. I think it exceeds this patch. > >> Reviewed-by: LIU Zhiwei > I posted a v3 based on Philippe's feedback. OK. Thanks Zhiwei > > Rich. > >> Zhiwei >> >>> RISCVExtStatus fs, vs; >>> uint32_t flags = 0;