Re: [PATCH 02/28] crypto: omap-sham: Don't idle/start SHA device between Encrypt operations

[Tero Kristo <t-kristo@ti.com>]

On 07/06/16 13:08, Herbert Xu wrote:
> On Wed, Jun 01, 2016 at 06:03:52PM -0500, Dave Gerlach wrote:
>> On 06/01/2016 04:53 AM, Grygorii Strashko wrote:
>>> On 06/01/2016 11:56 AM, Tero Kristo wrote:
>>>> From: Lokesh Vutla <lokeshvutla@ti.com>
>>>>
>>>> Calling runtime PM API for every block causes serious perf hit to
>>>> crypto operations that are done on a long buffer.
>>>> As crypto is performed on a page boundary, encrypting large buffers can
>>>> cause a series of crypto operations divided by page. The runtime PM API
>>>> is also called those many times.
>>>>
>>>> We call runtime_pm_get_sync only at beginning on the session (cra_init)
>>>> and runtime_pm_put at the end. This result in upto a 50% speedup.
>>>> This doesn't make the driver to keep the system awake as runtime get/put
>>>> is only called during a crypto session which completes usually quickly.
>>>>
>>>> Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
>>>> Signed-off-by: Tero Kristo <t-kristo@ti.com>
>>>> ---
>>>>   drivers/crypto/omap-sham.c | 27 +++++++++++++++++----------
>>>>   1 file changed, 17 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/crypto/omap-sham.c b/drivers/crypto/omap-sham.c
>>>> index 6eefaa2..bd0258f 100644
>>>> --- a/drivers/crypto/omap-sham.c
>>>> +++ b/drivers/crypto/omap-sham.c
>>>> @@ -360,14 +360,6 @@ static void omap_sham_copy_ready_hash(struct
>>>> ahash_request *req)
>>>>
>>>>   static int omap_sham_hw_init(struct omap_sham_dev *dd)
>>>>   {
>>>> -    int err;
>>>> -
>>>> -    err = pm_runtime_get_sync(dd->dev);
>>>> -    if (err < 0) {
>>>> -        dev_err(dd->dev, "failed to get sync: %d\n", err);
>>>> -        return err;
>>>> -    }
>>>> -
>>
>> Would it be worth it to investigate a pm_runtime autosuspend
>> approach rather than knocking runtime PM out here completely? I am
>> not clear if the overhead is coming from the pm_runtime calls
>> themselves or the actual idling of the IP, but if it's the idling of
>> the IP causing the slowdown, with a large enough autosuspend_delay
>> we don't actually sleep between each block but after a long enough
>> period of idle time we would actually suspend.
>
> Indeed, I think this patch is bogus.  cra_init is associated
> with the tfm object which is usually long-lived.  So doing power
> management there makes no sense.
>
> Cheers,
>

I can investigate this further, but I believe this patch itself gave a 
noticeable performance boost.

This is an optimization anyway, and not critical for functionality.

-Tero