> Isn't a thread likely to clear the AVX registers at the end of a function
> that uses them.
> In particular this removes the massive overhead on certain cpus of
> switching between two AVX modes.
> So it is actually unlikely that XSAVE will need to save them at all?
Only if context switches only
From: Aubrey Li
> Sent: 11 December 2018 00:25
>
> User space tools which do automated task placement need information
> about AVX-512 usage of tasks, because AVX-512 usage could cause core
> turbo frequency drop and impact the running task on the sibling CPU.
>
> The XSAVE hardware structure has
On 12/11/18 4:59 PM, Li, Aubrey wrote:
>> maybe instead of a 1/0 bit, it's useful to store the timestamp of the last
>> time we found the task to use avx? (need to find a good time unit)
>>
>>
> Are you suggesting kernel does not do any translation, just provide a fact
> to the user space tool and
On 2018/12/12 8:14, Arjan van de Ven wrote:
> On 12/11/2018 3:46 PM, Li, Aubrey wrote:
>> On 2018/12/12 1:18, Dave Hansen wrote:
>>> On 12/10/18 4:24 PM, Aubrey Li wrote:
The tracking turns on the usage flag at the next context switch of
the task, but requires 3 consecutive context switch
On 12/11/18 4:34 PM, Li, Aubrey wrote:
>> Is there a reason we shouldn't do:
>>
>> if (!cpu_feature_enabled(X86_FEATURE_AVX512F))
>> update_avx512_state(fpu);
>>
>> ?
>>
> Why _!_ ?
Sorry, got it backwards. I think I was considering having you do a
if (!cpu_feature_enab
On 2018/12/12 1:20, Dave Hansen wrote:
> to update AVX512 state
>> + */
>> +static inline void update_avx512_state(struct fpu *fpu)
>> +{
>> +/*
>> + * AVX512 state is tracked here because its use is known to slow
>> + * the max clock speed of the core.
>> + *
>> + * However, A
On 12/11/2018 3:46 PM, Li, Aubrey wrote:
On 2018/12/12 1:18, Dave Hansen wrote:
On 12/10/18 4:24 PM, Aubrey Li wrote:
The tracking turns on the usage flag at the next context switch of
the task, but requires 3 consecutive context switches with no usage
to clear it. This decay is required becaus
On 2018/12/12 1:18, Dave Hansen wrote:
> On 12/10/18 4:24 PM, Aubrey Li wrote:
>> The tracking turns on the usage flag at the next context switch of
>> the task, but requires 3 consecutive context switches with no usage
>> to clear it. This decay is required because well-written AVX-512
>> applicat
On Tue, Dec 11, 2018 at 09:18:25AM -0800, Dave Hansen wrote:
> On 12/10/18 4:24 PM, Aubrey Li wrote:
> > The tracking turns on the usage flag at the next context switch of
> > the task, but requires 3 consecutive context switches with no usage
> > to clear it. This decay is required because well-wr
On 12/11/18 9:18 AM, Dave Hansen wrote:
> On 12/10/18 4:24 PM, Aubrey Li wrote:
>> The tracking turns on the usage flag at the next context switch of
>> the task, but requires 3 consecutive context switches with no usage
>> to clear it. This decay is required because well-written AVX-512
>> appl
to update AVX512 state
> + */
> +static inline void update_avx512_state(struct fpu *fpu)
> +{
> + /*
> + * AVX512 state is tracked here because its use is known to slow
> + * the max clock speed of the core.
> + *
> + * However, AVX512-using tasks are expected to clear this
On 12/10/18 4:24 PM, Aubrey Li wrote:
> The tracking turns on the usage flag at the next context switch of
> the task, but requires 3 consecutive context switches with no usage
> to clear it. This decay is required because well-written AVX-512
> applications are expected to clear this state when no
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