* [PATCH v2] target/riscv: Use a direct cast for better performance @ 2023-10-08 21:50 Richard W.M. Jones 2023-10-08 21:50 ` Richard W.M. Jones 0 siblings, 1 reply; 6+ messages in thread From: Richard W.M. Jones @ 2023-10-08 21:50 UTC (permalink / raw) To: qemu-devel Cc: qemu-riscv, palmer, alistair.francis, bin.meng, liweiwei, dbarboza, zhiwei_liu, pbonzini v1 was here: https://lists.nongnu.org/archive/html/qemu-devel/2023-10/msg02021.html v2 is functionally exactly the same, except I changed s/qemu cast/QOM cast/ in the comment, and added the Reviewed-by tag received for the first version. Rich. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v2] target/riscv: Use a direct cast for better performance 2023-10-08 21:50 [PATCH v2] target/riscv: Use a direct cast for better performance Richard W.M. Jones @ 2023-10-08 21:50 ` Richard W.M. Jones 2023-10-09 10:23 ` Philippe Mathieu-Daudé 2023-10-09 12:36 ` LIU Zhiwei 0 siblings, 2 replies; 6+ messages in thread From: Richard W.M. Jones @ 2023-10-08 21:50 UTC (permalink / raw) To: qemu-devel Cc: qemu-riscv, palmer, alistair.francis, bin.meng, liweiwei, dbarboza, zhiwei_liu, pbonzini 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 <rjones@redhat.com> Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> --- 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; RISCVExtStatus fs, vs; uint32_t flags = 0; -- 2.41.0 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] target/riscv: Use a direct cast for better performance 2023-10-08 21:50 ` Richard W.M. Jones @ 2023-10-09 10:23 ` Philippe Mathieu-Daudé 2023-10-09 12:36 ` LIU Zhiwei 1 sibling, 0 replies; 6+ messages in thread From: Philippe Mathieu-Daudé @ 2023-10-09 10:23 UTC (permalink / raw) To: Richard W.M. Jones, qemu-devel Cc: qemu-riscv, palmer, alistair.francis, bin.meng, liweiwei, dbarboza, zhiwei_liu, pbonzini Hi Richard, On 8/10/23 23:50, 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 <rjones@redhat.com> > Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> > --- > 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); You might want to use: RISCVCPU *cpu = env_archcpu(env); Other occurences in target/riscv/internals.h. > + /* > + * 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; > RISCVExtStatus fs, vs; > uint32_t flags = 0; > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] target/riscv: Use a direct cast for better performance 2023-10-08 21:50 ` Richard W.M. Jones 2023-10-09 10:23 ` Philippe Mathieu-Daudé @ 2023-10-09 12:36 ` LIU Zhiwei 2023-10-09 12:53 ` Richard W.M. Jones 1 sibling, 1 reply; 6+ messages in thread From: LIU Zhiwei @ 2023-10-09 12:36 UTC (permalink / raw) To: Richard W.M. Jones, qemu-devel Cc: qemu-riscv, palmer, alistair.francis, bin.meng, liweiwei, dbarboza, pbonzini 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 <rjones@redhat.com> > Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> > --- > 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, Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com> Zhiwei > RISCVExtStatus fs, vs; > uint32_t flags = 0; > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] target/riscv: Use a direct cast for better performance 2023-10-09 12:36 ` LIU Zhiwei @ 2023-10-09 12:53 ` Richard W.M. Jones 2023-10-09 12:58 ` LIU Zhiwei 0 siblings, 1 reply; 6+ messages in thread From: Richard W.M. Jones @ 2023-10-09 12:53 UTC (permalink / raw) To: LIU Zhiwei Cc: qemu-devel, qemu-riscv, palmer, alistair.francis, bin.meng, liweiwei, dbarboza, pbonzini 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 <rjones@redhat.com> > >Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> > >--- > > 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) or here. If you have any suggestions I can try things. > Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com> I posted a v3 based on Philippe's feedback. Rich. > Zhiwei > > > RISCVExtStatus fs, vs; > > uint32_t flags = 0; -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] target/riscv: Use a direct cast for better performance 2023-10-09 12:53 ` Richard W.M. Jones @ 2023-10-09 12:58 ` LIU Zhiwei 0 siblings, 0 replies; 6+ messages in thread From: LIU Zhiwei @ 2023-10-09 12:58 UTC (permalink / raw) To: Richard W.M. Jones, LIU Zhiwei Cc: qemu-devel, qemu-riscv, palmer, alistair.francis, bin.meng, liweiwei, dbarboza, pbonzini 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 <rjones@redhat.com> >>> Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> >>> --- >>> 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 <zhiwei_liu@linux.alibaba.com> > I posted a v3 based on Philippe's feedback. OK. Thanks Zhiwei > > Rich. > >> Zhiwei >> >>> RISCVExtStatus fs, vs; >>> uint32_t flags = 0; ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-10-09 13:01 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2023-10-08 21:50 [PATCH v2] target/riscv: Use a direct cast for better performance Richard W.M. Jones 2023-10-08 21:50 ` Richard W.M. Jones 2023-10-09 10:23 ` Philippe Mathieu-Daudé 2023-10-09 12:36 ` LIU Zhiwei 2023-10-09 12:53 ` Richard W.M. Jones 2023-10-09 12:58 ` LIU Zhiwei
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