[PATCH 2/3] RISC-V: Detect unaligned vector accesses supported.
Jesse Taube
jesse at rivosinc.com
Fri Jun 7 13:11:04 PDT 2024
On 6/7/24 15:53, Jesse Taube wrote:
>
>
> On 6/6/24 19:13, Charlie Jenkins wrote:
>> On Thu, Jun 06, 2024 at 02:29:23PM -0700, Charlie Jenkins wrote:
>>> On Thu, Jun 06, 2024 at 02:32:14PM -0400, Jesse Taube wrote:
>>>> Run a unaligned vector access to test if the system supports
>>>> vector unaligned access. Add the result to a new key in hwprobe.
>>>> This is useful for usermode to know if vector misaligned accesses are
>>>> supported and if they are faster or slower than equivalent byte accesses.
>>>>
>>>> Signed-off-by: Jesse Taube <jesse at rivosinc.com>
>>>> ---
>>>> arch/riscv/include/asm/cpufeature.h | 2 +
>>>> arch/riscv/include/asm/hwprobe.h | 2 +-
>>>> arch/riscv/include/asm/vector.h | 1 +
>>>> arch/riscv/include/uapi/asm/hwprobe.h | 6 ++
>>>> arch/riscv/kernel/sys_hwprobe.c | 34 +++++++++
>>>> arch/riscv/kernel/traps_misaligned.c | 84 ++++++++++++++++++++--
>>>> arch/riscv/kernel/unaligned_access_speed.c | 4 ++
>>>> arch/riscv/kernel/vector.c | 2 +-
>>>> 8 files changed, 129 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
>>>> index 347805446151..a012c8490a27 100644
>>>> --- a/arch/riscv/include/asm/cpufeature.h
>>>> +++ b/arch/riscv/include/asm/cpufeature.h
>>>> @@ -35,9 +35,11 @@ void riscv_user_isa_enable(void);
>>>>
>>>> #if defined(CONFIG_RISCV_MISALIGNED)
>>>> bool check_unaligned_access_emulated_all_cpus(void);
>>>> +bool check_vector_unaligned_access_all_cpus(void);
>>>> void unaligned_emulation_finish(void);
>>>> bool unaligned_ctl_available(void);
>>>> DECLARE_PER_CPU(long, misaligned_access_speed);
>>>> +DECLARE_PER_CPU(long, vector_misaligned_access);
>>>> #else
>>>> static inline bool unaligned_ctl_available(void)
>>>> {
>>>> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
>>>> index 630507dff5ea..150a9877b0af 100644
>>>> --- a/arch/riscv/include/asm/hwprobe.h
>>>> +++ b/arch/riscv/include/asm/hwprobe.h
>>>> @@ -8,7 +8,7 @@
>>>>
>>>> #include <uapi/asm/hwprobe.h>
>>>>
>>>> -#define RISCV_HWPROBE_MAX_KEY 6
>>>> +#define RISCV_HWPROBE_MAX_KEY 7
>>>>
>>>> static inline bool riscv_hwprobe_key_is_valid(__s64 key)
>>>> {
>>>> diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
>>>> index 731dcd0ed4de..776af9b37e23 100644
>>>> --- a/arch/riscv/include/asm/vector.h
>>>> +++ b/arch/riscv/include/asm/vector.h
>>>> @@ -21,6 +21,7 @@
>>>>
>>>> extern unsigned long riscv_v_vsize;
>>>> int riscv_v_setup_vsize(void);
>>>> +bool insn_is_vector(u32 insn_buf);
>>>> bool riscv_v_first_use_handler(struct pt_regs *regs);
>>>> void kernel_vector_begin(void);
>>>> void kernel_vector_end(void);
>>>> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
>>>> index 060212331a03..ebacff86f134 100644
>>>> --- a/arch/riscv/include/uapi/asm/hwprobe.h
>>>> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
>>>> @@ -68,6 +68,12 @@ struct riscv_hwprobe {
>>>> #define RISCV_HWPROBE_MISALIGNED_UNSUPPORTED (4 << 0)
>>>> #define RISCV_HWPROBE_MISALIGNED_MASK (7 << 0)
>>>> #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE 6
>>>> +#define RISCV_HWPROBE_VEC_KEY_MISALIGNED_PERF 7
>>>> +#define RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN 0
>>>> +#define RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED 1
>>>> +#define RISCV_HWPROBE_VEC_MISALIGNED_SLOW 2
>>>> +#define RISCV_HWPROBE_VEC_MISALIGNED_FAST 3
>>>> +#define RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED 4
>>>> /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
>>>>
>>>> /* Flags */
>>>> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
>>>> index b286b73e763e..ce641cc6e47a 100644
>>>> --- a/arch/riscv/kernel/sys_hwprobe.c
>>>> +++ b/arch/riscv/kernel/sys_hwprobe.c
>>>> @@ -184,6 +184,36 @@ static u64 hwprobe_misaligned(const struct cpumask *cpus)
>>>> }
>>>> #endif
>>>>
>>>> +#if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS)
>>>> +static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
>>>> +{
>>>> + int cpu;
>>>> + u64 perf = -1ULL;
>>>> +
>>>> + for_each_cpu(cpu, cpus) {
>>>> + int this_perf = per_cpu(vector_misaligned_access, cpu);
>>>> +
>>>> + if (perf == -1ULL)
>>>> + perf = this_perf;
>>>> +
>>>> + if (perf != this_perf) {
>>>> + perf = RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>>> + break;
>>>> + }
>>>> + }
>>>> +
>>>> + if (perf == -1ULL)
>>>> + return RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>>> +
>>>> + return perf;
>>>> +}
>>>> +#else
>>>> +static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
>>>> +{
>>
>> I meant to mention this in my last message!
>>
>> The scalar version has cutouts for configs here like:
>>
>> if (IS_ENABLED(CONFIG_RISCV_EFFICIENT_UNALIGNED_ACCESS))
>> return RISCV_HWPROBE_MISALIGNED_FAST;
>>
>
For both scalar and vector CONFIG_RISCV_PROBE_UNALIGNED_ACCESS probes
the speed not support. So misaligned_access_speed will have a valid value.
```
if (IS_ENABLED(CONFIG_RISCV_EFFICIENT_VEC_UNALIGNED_ACCESS))
return RISCV_HWPROBE_MISALIGNED_FAST;
if(IS_ENABLED(CONFIG_RISCV_SLOW_VEC_UNALIGNED_ACCESS))
return RISCV_HWPROBE_VEC_MISALIGNED_SLOW;
if(IS_ENABLED(CONFIG_RISCV_VEC_UNALIGNED_ACCESS))
/* Sence we cant gurentee that we do have UNALIGNED_ACCESS we can return
the result from the test */
return per_cpu(vector_misaligned_access, cpu);
return RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
```
> Will add
>
>> Having this functionality on vector as well would be much appreciated.
>> I don't think it's valid to assume that vector and scalar have the same
>> speed, so this would require a vector version of the RISCV_MISALIGNED
>> tree in arch/riscv/Kconfig.
>>
>> - Charlie
>>
>>>> + return RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>>> +}
>>>> +#endif
>>>> +
>>>> static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>>>> const struct cpumask *cpus)
>>>> {
>>>> @@ -211,6 +241,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>>>> pair->value = hwprobe_misaligned(cpus);
>>>> break;
>>>>
>>>> + case RISCV_HWPROBE_VEC_KEY_MISALIGNED_PERF:
>>>> + pair->value = hwprobe_vec_misaligned(cpus);
>>>> + break;
>>>> +
>>>> case RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE:
>>>> pair->value = 0;
>>>> if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
>>>> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
>>>> index 2adb7c3e4dd5..8f26c3d92230 100644
>>>> --- a/arch/riscv/kernel/traps_misaligned.c
>>>> +++ b/arch/riscv/kernel/traps_misaligned.c
>>>> @@ -16,6 +16,7 @@
>>>> #include <asm/entry-common.h>
>>>> #include <asm/hwprobe.h>
>>>> #include <asm/cpufeature.h>
>>>> +#include <asm/vector.h>
>>>>
>>>> #define INSN_MATCH_LB 0x3
>>>> #define INSN_MASK_LB 0x707f
>>>> @@ -413,10 +414,6 @@ int handle_misaligned_load(struct pt_regs *regs)
>>>>
>>>> perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
>>>>
>>>> -#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>>>> - *this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_EMULATED;
>>>> -#endif
>>>> -
>>>> if (!unaligned_enabled)
>>>> return -1;
>>>>
>>>> @@ -426,6 +423,17 @@ int handle_misaligned_load(struct pt_regs *regs)
>>>> if (get_insn(regs, epc, &insn))
>>>> return -1;
>>>>
>>>> +#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>>>> + if (insn_is_vector(insn) &&
>>>> + *this_cpu_ptr(&vector_misaligned_access) == RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED) {
>>>> + *this_cpu_ptr(&vector_misaligned_access) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>> + regs->epc = epc + INSN_LEN(insn);
>>>> + return 0;
>
> There is a return before scalar speed is set.
>
>>>> + }
>>>> +
>>>> + *this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_EMULATED;
>>>
>>> This unconditionally sets scalar unaligned accesses even if the
>>> unaligned access is caused by vector. Scalar unaligned accesses should
>>> only be set to emulated if this function is entered from a scalar
>>> unaligned load.
>>>
>>> The rest of this function handles how scalar unaligned accesses are
>>> emulated, and the equivalent needs to happen for vector. You need to add
>>> routines that manually load the data from the memory address into the
>>> vector register. When Clément did this for scalar, he provided a test
>>> case to help reviewers [1]. Please add onto these test cases or make
>>> your own for vector.
>
> I wansnt planing on adding emulation in this patch. I can if needed.
>
>>>
>>> Link: https://github.com/clementleger/unaligned_test [1]
>>>
>>>> +#endif
>>>> +
>>>> regs->epc = 0;
>>>>
>>>> if ((insn & INSN_MASK_LW) == INSN_MATCH_LW) {
>>>> @@ -625,6 +633,74 @@ static bool check_unaligned_access_emulated(int cpu)
>>>> return misaligned_emu_detected;
>>>> }
>>>>
>>>> +#ifdef CONFIG_RISCV_ISA_V
>>>> +static void check_vector_unaligned_access(struct work_struct *unused)
>>>
>>> Can you standardize this name with the scalar version by writing
>>> emulated in it?
>
> We dont emulate it so that wouldn't make sence.
>
>>>
>>> "check_vector_unaligned_access_emulated_all_cpus"
>>>
>>>> +{
>>>> + int cpu = smp_processor_id();
>>>> + long *mas_ptr = this_cpu_ptr(&vector_misaligned_access);
>>>> + unsigned long tmp_var;
>>>> +
>>>> + if (!riscv_isa_extension_available(hart_isa[cpu].isa, v))
>>>> + return;
>>>> +
>>>> + *mas_ptr = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>>>> +
>>>> + local_irq_enable();
>>>> + kernel_vector_begin();
>>>> + __asm__ __volatile__ (
>>>> + ".balign 4\n\t"
>>>> + ".option push\n\t"
>>>> + ".option arch, +v\n\t"
>>>> + " vsetivli zero, 1, e16, m1, ta, ma\n\t" // Vectors of 16b
>>>> + " vle16.v v0, (%[ptr])\n\t" // Load bytes
>>>> + ".option pop\n\t"
>>>> + : : [ptr] "r" ((u8 *)&tmp_var + 1) : "v0", "memory");
>>>
>>> memory is being read from, but not written to, so there is no need to
>>> have a memory clobber.
>
> fixed.
>
>>>
>>>> + kernel_vector_end();
>>>> +
>>>> + if (*mas_ptr == RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN)
>>>> + *mas_ptr = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>>>> +}
>>>> +
>>>> +bool check_vector_unaligned_access_all_cpus(void)
>>>> +{
>>>> + int cpu;
>>>> + bool ret = true;
>>>> +
>>>> + for_each_online_cpu(cpu)
>>>> + if (riscv_isa_extension_available(hart_isa[cpu].isa, ZICCLSM))
>>>
>>> zicclsm is not specific to vector so it can be extracted out of this
>>> vector specific function. Assuming that hardware properly reports the
>>> extension, if zicclsm is present then it is known that both vector and
>>> scalar unaligned accesses are supported.
>
> Added so we don't need to waste cycles testing support.
>
>>>> + per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>>>
>>> Please use the exising UNKNOWN terminology instead of renaming to
>>> SUPPORTED. Any option that is not UNSUPPORTED implies that unaligned
>>> accesses are supported.
>
> Conor didnt like using UNKNOWN a proxy for "SUPPORTED"
> Having SUPPORTED is better then assuing the speed to be slow.
>
>>>
>>>> + else
>>>> + ret = false;
>>>> +
>>>> +
>>>> + if (ret)
>>>> + return true;
>>>> + ret = true;
>>>> +
>>>> + schedule_on_each_cpu(check_vector_unaligned_access);
>>>> +
>>>> + for_each_online_cpu(cpu)
>>>> + if (per_cpu(vector_misaligned_access, cpu)
>>>> + != RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED)
>>>> + return false;
>>>> +
>>>> + return ret;
>>>> +}
>>>> +#else
>>>
>>> If CONFIG_RISCV_ISA_V is not set, there is no value in checking if
>>> vector unaligned accesses are supported because userspace will not be
>>> allowed to use vector instructions anyway.
>
> Oh I'm silly meant to be seting to all UNSUPPORTED.
>
>
> Thanks,
> Jesse Taube
>
>>>
>>> - Charlie
>>>
>>>> +bool check_vector_unaligned_access_all_cpus(void)
>>>> +{
>>>> + int cpu;
>>>> +
>>>> + for_each_online_cpu(cpu)
>>>> + if (riscv_isa_extension_available(hart_isa[cpu].isa, ZICCLSM))
>>>> + per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>>>> + else
>>>> + per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>> +
>>>> + return false;
>>>> +}
>>>> +#endif
>>>> +
>>>> bool check_unaligned_access_emulated_all_cpus(void)
>>>> {
>>>> int cpu;
>>>> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
>>>> index a9a6bcb02acf..92a84239beaa 100644
>>>> --- a/arch/riscv/kernel/unaligned_access_speed.c
>>>> +++ b/arch/riscv/kernel/unaligned_access_speed.c
>>>> @@ -20,6 +20,7 @@
>>>> #define MISALIGNED_COPY_SIZE ((MISALIGNED_BUFFER_SIZE / 2) - 0x80)
>>>>
>>>> DEFINE_PER_CPU(long, misaligned_access_speed);
>>>> +DEFINE_PER_CPU(long, vector_misaligned_access) = RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>>>
>>>> #ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>>>> static cpumask_t fast_misaligned_access;
>>>> @@ -264,6 +265,8 @@ static int check_unaligned_access_all_cpus(void)
>>>> {
>>>> bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
>>>>
>>>> + check_vector_unaligned_access_all_cpus();
>>>> +
>>>> if (!all_cpus_emulated)
>>>> return check_unaligned_access_speed_all_cpus();
>>>>
>>>> @@ -273,6 +276,7 @@ static int check_unaligned_access_all_cpus(void)
>>>> static int check_unaligned_access_all_cpus(void)
>>>> {
>>>> check_unaligned_access_emulated_all_cpus();
>>>> + check_vector_unaligned_access_all_cpus();
>>>>
>>>> return 0;
>>>> }
>>>> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
>>>> index 6727d1d3b8f2..2cceab739b2c 100644
>>>> --- a/arch/riscv/kernel/vector.c
>>>> +++ b/arch/riscv/kernel/vector.c
>>>> @@ -66,7 +66,7 @@ void __init riscv_v_setup_ctx_cache(void)
>>>> #endif
>>>> }
>>>>
>>>> -static bool insn_is_vector(u32 insn_buf)
>>>> +bool insn_is_vector(u32 insn_buf)
>>>> {
>>>> u32 opcode = insn_buf & __INSN_OPCODE_MASK;
>>>> u32 width, csr;
>>>> --
>>>> 2.43.0
>>>>
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