Re: [PATCH net-next 1/3] perf, events: add non-linear data support for raw records

From: Daniel Borkmann
Date: Wed Jul 13 2016 - 12:53:48 EST


On 07/13/2016 06:40 PM, Peter Zijlstra wrote:
On Wed, Jul 13, 2016 at 04:08:55PM +0200, Daniel Borkmann wrote:
On 07/13/2016 03:42 PM, Peter Zijlstra wrote:

Ok so the nonlinear thing was it doing _two_ copies, one the regular
__output_copy() on raw->data and second the optional fragment thingy
using __output_custom().

Would something like this work instead?

It does the nonlinear thing and the custom copy function thing but
allows more than 2 fragments and allows each fragment to have a custom
copy.

It doesn't look obviously more expensive; it has the one ->copy branch
extra, but then it doesn't recompute the sizes.

Yes, that would work as well on a quick glance with diff just a bit
bigger, but more generic this way. Do you want me to adapt this into
the first patch?

Please.

One question below:


- u64 zero = 0;

- if (real_size - raw_size)
- __output_copy(handle, &zero, real_size - raw_size);

We still need the zero padding here from above with the computed
raw->size, right?

Ah, yes, we need some __output*() in order to advance the handle offset.
We don't _need_ to copy the 0s, but I doubt __output_skip() is much
cheaper for these 1-3 bytes worth of data; we've already touched that
line anyway.

Okay, thanks for your input! I'll respin then.