| Message ID | 20210723203344.968563-4-richard.henderson@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | target/arm: Add sve-default-vector-length cpu property | expand |
On Fri, 23 Jul 2021 at 21:36, Richard Henderson <richard.henderson@linaro.org> wrote: > > Mirror the behavour of /proc/sys/abi/sve_default_vector_length > under the real linux kernel. We have no way of passing along > a real default across exec like the kernel can, but this is a > decent way of adjusting the startup vector length of a process. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/482 > Signed-off-by: Richard Henderson <richard.henderson@linaro.org> > --- > docs/system/arm/cpu-features.rst | 11 ++++++ > target/arm/cpu.h | 5 +++ > target/arm/cpu.c | 14 ++++++-- > target/arm/cpu64.c | 60 ++++++++++++++++++++++++++++++++ > 4 files changed, 88 insertions(+), 2 deletions(-) > > diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst > index c455442eaf..4ff36cc83f 100644 > --- a/docs/system/arm/cpu-features.rst > +++ b/docs/system/arm/cpu-features.rst > @@ -376,3 +376,14 @@ verbose command lines. However, the recommended way to select vector > lengths is to explicitly enable each desired length. Therefore only > example's (1), (4), and (6) exhibit recommended uses of the properties. > > +SVE User-mode Default Vector Length Property > +-------------------------------------------- > + > +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is You probably don't want single-backticks. In rST this means "interpreted text", which can be handled as a bunch of different things if tagged with a specific "role": https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text The default "role" if none is specified is "title_reference", intended for references to book or article titles, and it renders into the HTML as <cite>...</cite> (usually comes out as italics). If you want fixed-width-font text, that's double backtick: ``text``. If you want italics, that's *emphasised text*. If you want bold, that's **strong text**. > +defined to mirror the Linux kernel parameter file > +`/proc/sys/abi/sve_default_vector_length`. The default length, `N`, > +is in units of bytes and must be between 16 and 8192. > +If not specified, the default vector length is 64. > + > +If the default length is larger than the maximum vector length enabled > +with `sve<N>` properties, the actual vector length will be reduced. We should document the -1 case too, something like: If this property is set to ``-1`` then the default vector length is set to the maximum possible length. Otherwise Reviewed-by: Peter Maydell <peter.maydell@linaro.org> thanks -- PMM
On Fri, Jul 23, 2021 at 10:33:44AM -1000, Richard Henderson wrote: > Mirror the behavour of /proc/sys/abi/sve_default_vector_length > under the real linux kernel. We have no way of passing along > a real default across exec like the kernel can, but this is a > decent way of adjusting the startup vector length of a process. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/482 > Signed-off-by: Richard Henderson <richard.henderson@linaro.org> > --- > docs/system/arm/cpu-features.rst | 11 ++++++ > target/arm/cpu.h | 5 +++ > target/arm/cpu.c | 14 ++++++-- > target/arm/cpu64.c | 60 ++++++++++++++++++++++++++++++++ > 4 files changed, 88 insertions(+), 2 deletions(-) > > diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst > index c455442eaf..4ff36cc83f 100644 > --- a/docs/system/arm/cpu-features.rst > +++ b/docs/system/arm/cpu-features.rst > @@ -376,3 +376,14 @@ verbose command lines. However, the recommended way to select vector > lengths is to explicitly enable each desired length. Therefore only > example's (1), (4), and (6) exhibit recommended uses of the properties. > > +SVE User-mode Default Vector Length Property > +-------------------------------------------- > + > +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is > +defined to mirror the Linux kernel parameter file > +`/proc/sys/abi/sve_default_vector_length`. The default length, `N`, > +is in units of bytes and must be between 16 and 8192. Hmm. If a user inputs anything greater than 256, then won't it get silently reduced to 256? > +If not specified, the default vector length is 64. > + > +If the default length is larger than the maximum vector length enabled > +with `sve<N>` properties, the actual vector length will be reduced. Here it's pointed out that the default may be reduced, but it implies that that only happens if an sve<N> property is also given. Won't users wonder why they're only getting vectors that are 256 bytes large even when they ask for more? Thanks, drew > diff --git a/target/arm/cpu.h b/target/arm/cpu.h > index be9a4dceae..9f0a5f84d5 100644 > --- a/target/arm/cpu.h > +++ b/target/arm/cpu.h > @@ -1006,6 +1006,11 @@ struct ARMCPU { > /* Used to set the maximum vector length the cpu will support. */ > uint32_t sve_max_vq; > > +#ifdef CONFIG_USER_ONLY > + /* Used to set the default vector length at process start. */ > + uint32_t sve_default_vq; > +#endif > + > /* > * In sve_vq_map each set bit is a supported vector length of > * (bit-number + 1) * 16 bytes, i.e. each bit number + 1 is the vector > diff --git a/target/arm/cpu.c b/target/arm/cpu.c > index 752b15bb79..2866dd7658 100644 > --- a/target/arm/cpu.c > +++ b/target/arm/cpu.c > @@ -201,7 +201,8 @@ static void arm_cpu_reset(DeviceState *dev) > env->cp15.cpacr_el1 = deposit64(env->cp15.cpacr_el1, 16, 2, 3); > /* with reasonable vector length */ > if (cpu_isar_feature(aa64_sve, cpu)) { > - env->vfp.zcr_el[1] = MIN(cpu->sve_max_vq - 1, 3); > + env->vfp.zcr_el[1] = > + aarch64_sve_zcr_get_valid_len(cpu, cpu->sve_default_vq - 1); > } > /* > * Enable TBI0 but not TBI1. > @@ -1051,7 +1052,16 @@ static void arm_cpu_initfn(Object *obj) > QLIST_INIT(&cpu->pre_el_change_hooks); > QLIST_INIT(&cpu->el_change_hooks); > > -#ifndef CONFIG_USER_ONLY > +#ifdef CONFIG_USER_ONLY > +# ifdef TARGET_AARCH64 > + /* > + * The linux kernel defaults to 512-bit vectors, when sve is supported. > + * See documentation for /proc/sys/abi/sve_default_vector_length, and > + * our corresponding sve-default-vector-length cpu property. > + */ > + cpu->sve_default_vq = 4; > +# endif > +#else > /* Our inbound IRQ and FIQ lines */ > if (kvm_enabled()) { > /* VIRQ and VFIQ are unused with KVM but we add them to maintain > diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c > index c7a1626bec..c690318a9b 100644 > --- a/target/arm/cpu64.c > +++ b/target/arm/cpu64.c > @@ -559,6 +559,59 @@ static void cpu_arm_set_sve(Object *obj, bool value, Error **errp) > cpu->isar.id_aa64pfr0 = t; > } > > +#ifdef CONFIG_USER_ONLY > +/* Mirror linux /proc/sys/abi/sve_default_vector_length. */ > +static void cpu_arm_set_sve_default_vec_len(Object *obj, Visitor *v, > + const char *name, void *opaque, > + Error **errp) > +{ > + ARMCPU *cpu = ARM_CPU(obj); > + int32_t default_len, default_vq, remainder; > + > + if (!visit_type_int32(v, name, &default_len, errp)) { > + return; > + } > + > + /* Undocumented, but the kernel allows -1 to indicate "maximum". */ > + if (default_len == -1) { > + cpu->sve_default_vq = ARM_MAX_VQ; > + return; > + } > + > + default_vq = default_len / 16; > + remainder = default_len % 16; > + > + /* > + * Note that the 512 max comes from include/uapi/asm/sve_context.h > + * and is the maximum architectural width of ZCR_ELx.LEN. > + */ > + if (remainder || default_vq < 1 || default_vq > 512) { > + error_setg(errp, "cannot set sve-default-vector-length"); > + if (remainder) { > + error_append_hint(errp, "Vector length not a multiple of 16\n"); > + } else if (default_vq < 1) { > + error_append_hint(errp, "Vector length smaller than 16\n"); > + } else { > + error_append_hint(errp, "Vector length larger than %d\n", > + 512 * 16); > + } > + return; > + } > + > + cpu->sve_default_vq = default_vq; > +} > + > +static void cpu_arm_get_sve_default_vec_len(Object *obj, Visitor *v, > + const char *name, void *opaque, > + Error **errp) > +{ > + ARMCPU *cpu = ARM_CPU(obj); > + int32_t value = cpu->sve_default_vq * 16; > + > + visit_type_int32(v, name, &value, errp); > +} > +#endif > + > void aarch64_add_sve_properties(Object *obj) > { > uint32_t vq; > @@ -571,6 +624,13 @@ void aarch64_add_sve_properties(Object *obj) > object_property_add(obj, name, "bool", cpu_arm_get_sve_vq, > cpu_arm_set_sve_vq, NULL, NULL); > } > + > +#ifdef CONFIG_USER_ONLY > + /* Mirror linux /proc/sys/abi/sve_default_vector_length. */ > + object_property_add(obj, "sve-default-vector-length", "int32", > + cpu_arm_get_sve_default_vec_len, > + cpu_arm_set_sve_default_vec_len, NULL, NULL); > +#endif > } > > void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp) > -- > 2.25.1 > >
On 7/26/21 4:59 AM, Andrew Jones wrote: >> +SVE User-mode Default Vector Length Property >> +-------------------------------------------- >> + >> +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is >> +defined to mirror the Linux kernel parameter file >> +`/proc/sys/abi/sve_default_vector_length`. The default length, `N`, >> +is in units of bytes and must be between 16 and 8192. > > Hmm. If a user inputs anything greater than 256, then won't it get > silently reduced to 256? Yes. >> +If not specified, the default vector length is 64. >> + >> +If the default length is larger than the maximum vector length enabled >> +with `sve<N>` properties, the actual vector length will be reduced. > > Here it's pointed out that the default may be reduced, but it implies that > that only happens if an sve<N> property is also given. Won't users wonder > why they're only getting vectors that are 256 bytes large even when they > ask for more? I guess adding that 256 is the maximum length supported by qemu should be sufficient? r~
On Mon, Jul 26, 2021 at 08:33:52AM -1000, Richard Henderson wrote: > On 7/26/21 4:59 AM, Andrew Jones wrote: > > > +SVE User-mode Default Vector Length Property > > > +-------------------------------------------- > > > + > > > +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is > > > +defined to mirror the Linux kernel parameter file > > > +`/proc/sys/abi/sve_default_vector_length`. The default length, `N`, > > > +is in units of bytes and must be between 16 and 8192. > > > > Hmm. If a user inputs anything greater than 256, then won't it get > > silently reduced to 256? > > Yes. > > > > +If not specified, the default vector length is 64. > > > + > > > +If the default length is larger than the maximum vector length enabled > > > +with `sve<N>` properties, the actual vector length will be reduced. > > > > Here it's pointed out that the default may be reduced, but it implies that > > that only happens if an sve<N> property is also given. Won't users wonder > > why they're only getting vectors that are 256 bytes large even when they > > ask for more? > > I guess adding that 256 is the maximum length supported by qemu should be sufficient? > Works for me. Thanks, drew
On Mon, 26 Jul 2021 at 19:34, Richard Henderson <richard.henderson@linaro.org> wrote: > > On 7/26/21 4:59 AM, Andrew Jones wrote: > >> +SVE User-mode Default Vector Length Property > >> +-------------------------------------------- > >> + > >> +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is > >> +defined to mirror the Linux kernel parameter file > >> +`/proc/sys/abi/sve_default_vector_length`. The default length, `N`, > >> +is in units of bytes and must be between 16 and 8192. > > > > Hmm. If a user inputs anything greater than 256, then won't it get > > silently reduced to 256? > > Yes. > > >> +If not specified, the default vector length is 64. > >> + > >> +If the default length is larger than the maximum vector length enabled > >> +with `sve<N>` properties, the actual vector length will be reduced. > > > > Here it's pointed out that the default may be reduced, but it implies that > > that only happens if an sve<N> property is also given. Won't users wonder > > why they're only getting vectors that are 256 bytes large even when they > > ask for more? > > I guess adding that 256 is the maximum length supported by qemu should be sufficient? Could you either provide a fixup diff for me to fold into this patch or else repost a new version? (I don't mind which; if it's just a docs tweak fixup diff is probably simplest.) thanks -- PMM
diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst index c455442eaf..4ff36cc83f 100644 --- a/docs/system/arm/cpu-features.rst +++ b/docs/system/arm/cpu-features.rst @@ -376,3 +376,14 @@ verbose command lines. However, the recommended way to select vector lengths is to explicitly enable each desired length. Therefore only example's (1), (4), and (6) exhibit recommended uses of the properties. +SVE User-mode Default Vector Length Property +-------------------------------------------- + +For qemu-aarch64, the cpu property `sve-default-vector-length=N` is +defined to mirror the Linux kernel parameter file +`/proc/sys/abi/sve_default_vector_length`. The default length, `N`, +is in units of bytes and must be between 16 and 8192. +If not specified, the default vector length is 64. + +If the default length is larger than the maximum vector length enabled +with `sve<N>` properties, the actual vector length will be reduced. diff --git a/target/arm/cpu.h b/target/arm/cpu.h index be9a4dceae..9f0a5f84d5 100644 --- a/target/arm/cpu.h +++ b/target/arm/cpu.h @@ -1006,6 +1006,11 @@ struct ARMCPU { /* Used to set the maximum vector length the cpu will support. */ uint32_t sve_max_vq; +#ifdef CONFIG_USER_ONLY + /* Used to set the default vector length at process start. */ + uint32_t sve_default_vq; +#endif + /* * In sve_vq_map each set bit is a supported vector length of * (bit-number + 1) * 16 bytes, i.e. each bit number + 1 is the vector diff --git a/target/arm/cpu.c b/target/arm/cpu.c index 752b15bb79..2866dd7658 100644 --- a/target/arm/cpu.c +++ b/target/arm/cpu.c @@ -201,7 +201,8 @@ static void arm_cpu_reset(DeviceState *dev) env->cp15.cpacr_el1 = deposit64(env->cp15.cpacr_el1, 16, 2, 3); /* with reasonable vector length */ if (cpu_isar_feature(aa64_sve, cpu)) { - env->vfp.zcr_el[1] = MIN(cpu->sve_max_vq - 1, 3); + env->vfp.zcr_el[1] = + aarch64_sve_zcr_get_valid_len(cpu, cpu->sve_default_vq - 1); } /* * Enable TBI0 but not TBI1. @@ -1051,7 +1052,16 @@ static void arm_cpu_initfn(Object *obj) QLIST_INIT(&cpu->pre_el_change_hooks); QLIST_INIT(&cpu->el_change_hooks); -#ifndef CONFIG_USER_ONLY +#ifdef CONFIG_USER_ONLY +# ifdef TARGET_AARCH64 + /* + * The linux kernel defaults to 512-bit vectors, when sve is supported. + * See documentation for /proc/sys/abi/sve_default_vector_length, and + * our corresponding sve-default-vector-length cpu property. + */ + cpu->sve_default_vq = 4; +# endif +#else /* Our inbound IRQ and FIQ lines */ if (kvm_enabled()) { /* VIRQ and VFIQ are unused with KVM but we add them to maintain diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c index c7a1626bec..c690318a9b 100644 --- a/target/arm/cpu64.c +++ b/target/arm/cpu64.c @@ -559,6 +559,59 @@ static void cpu_arm_set_sve(Object *obj, bool value, Error **errp) cpu->isar.id_aa64pfr0 = t; } +#ifdef CONFIG_USER_ONLY +/* Mirror linux /proc/sys/abi/sve_default_vector_length. */ +static void cpu_arm_set_sve_default_vec_len(Object *obj, Visitor *v, + const char *name, void *opaque, + Error **errp) +{ + ARMCPU *cpu = ARM_CPU(obj); + int32_t default_len, default_vq, remainder; + + if (!visit_type_int32(v, name, &default_len, errp)) { + return; + } + + /* Undocumented, but the kernel allows -1 to indicate "maximum". */ + if (default_len == -1) { + cpu->sve_default_vq = ARM_MAX_VQ; + return; + } + + default_vq = default_len / 16; + remainder = default_len % 16; + + /* + * Note that the 512 max comes from include/uapi/asm/sve_context.h + * and is the maximum architectural width of ZCR_ELx.LEN. + */ + if (remainder || default_vq < 1 || default_vq > 512) { + error_setg(errp, "cannot set sve-default-vector-length"); + if (remainder) { + error_append_hint(errp, "Vector length not a multiple of 16\n"); + } else if (default_vq < 1) { + error_append_hint(errp, "Vector length smaller than 16\n"); + } else { + error_append_hint(errp, "Vector length larger than %d\n", + 512 * 16); + } + return; + } + + cpu->sve_default_vq = default_vq; +} + +static void cpu_arm_get_sve_default_vec_len(Object *obj, Visitor *v, + const char *name, void *opaque, + Error **errp) +{ + ARMCPU *cpu = ARM_CPU(obj); + int32_t value = cpu->sve_default_vq * 16; + + visit_type_int32(v, name, &value, errp); +} +#endif + void aarch64_add_sve_properties(Object *obj) { uint32_t vq; @@ -571,6 +624,13 @@ void aarch64_add_sve_properties(Object *obj) object_property_add(obj, name, "bool", cpu_arm_get_sve_vq, cpu_arm_set_sve_vq, NULL, NULL); } + +#ifdef CONFIG_USER_ONLY + /* Mirror linux /proc/sys/abi/sve_default_vector_length. */ + object_property_add(obj, "sve-default-vector-length", "int32", + cpu_arm_get_sve_default_vec_len, + cpu_arm_set_sve_default_vec_len, NULL, NULL); +#endif } void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp)
Mirror the behavour of /proc/sys/abi/sve_default_vector_length under the real linux kernel. We have no way of passing along a real default across exec like the kernel can, but this is a decent way of adjusting the startup vector length of a process. Resolves: https://gitlab.com/qemu-project/qemu/-/issues/482 Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- docs/system/arm/cpu-features.rst | 11 ++++++ target/arm/cpu.h | 5 +++ target/arm/cpu.c | 14 ++++++-- target/arm/cpu64.c | 60 ++++++++++++++++++++++++++++++++ 4 files changed, 88 insertions(+), 2 deletions(-)