Subject: RE: [PATCH v24 03/20] iov_iter: skip copy if src == dst for direct data placement

From: Aurelien Aptel <[email-masked]>
Date: Thu, 18 Apr 2024 11:22:42 +0300

Hi David,

David Laight <[email-masked]> writes:
> How must does this conditional cost for the normal case
> when it is true?
> I suspect it is mispredicted 50% of the time.
> So, while it may speed up your test, the overall system
> impact will be negative.

We have done some measures to evaluate the cost of the additional test
and we don't see any noticeable impact on performances.

If this is still a concern, we can add compilation-time check on
CONFIG_ULP_DDP i.e. ifdef or IS_ENABLED() (which gets optimized out).

Thanks