Re: [igt-dev] [PATCH V6 i-g-t 3/6] lib: Add function to hash a framebuffer

Rodrigo Siqueira
2019-07-12T02:49:41Z

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On 07/10, Ser, Simon wrote:
> On Wed, 2019-07-10 at 15:30 +0000, Ser, Simon wrote:
> > Mostly LGTM, here are a few nits.
> >
> > On Wed, 2019-06-12 at 23:17 -0300, Brian Starkey wrote:
> > > To use writeback buffers as a CRC source, we need to be able to hash
> > > them. Implement a simple FVA-1a hashing routine for this purpose.
> > >
> > > Doing a bytewise hash on the framebuffer directly can be very slow if
> > > the memory is noncached. By making a copy of each line in the FB first
> > > (which can take advantage of word-access speedup), we can do the hash
> > > on a cached copy, which is much faster (10x speedup on my platform).
> > >
> > > v6: use igt_memcpy_from_wc() instead of plain memcpy, as suggested by
> > > Chris Wilson
> > >
> > > Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> > > [rebased and updated to the most recent API]
> > > Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
> > > ---
> > > lib/igt_fb.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > lib/igt_fb.h | 3 +++
> > > 2 files changed, 69 insertions(+)
> > >
> > > diff --git a/lib/igt_fb.c b/lib/igt_fb.c
> > > index 9d4f905e..d07dae39 100644
> > > --- a/lib/igt_fb.c
> > > +++ b/lib/igt_fb.c
> > > @@ -3256,6 +3256,72 @@ bool igt_fb_supported_format(uint32_t drm_format)
> > > return false;
> > > }
> > >
> > > +/*
> > > + * This implements the FNV-1a hashing algorithm instead of CRC, for
> > > + * simplicity
> > > + * http://www.isthe.com/chongo/tech/comp/fnv/index.html
> > > + *
> > > + * hash = offset_basis
> > > + * for each octet_of_data to be hashed
> > > + * hash = hash xor octet_of_data
> > > + * hash = hash * FNV_prime
> > > + * return hash
> > > + *
> > > + * 32 bit offset_basis = 2166136261
> > > + * 32 bit FNV_prime = 224 + 28 + 0x93 = 16777619
> > > + */
> > > +int igt_fb_get_crc(struct igt_fb *fb, igt_crc_t *crc)
> > > +{
> > > +#define FNV1a_OFFSET_BIAS 2166136261
> > > +#define FNV1a_PRIME 16777619
> >
> > I'd just use plain uint32_t variables for those, but no big deal.
> >
> > > + uint32_t hash;
> > > + void *map;
> > > + char *ptr, *line = NULL;
> > > + int x, y, cpp = igt_drm_format_to_bpp(fb->drm_format) / 8;
> > > + uint32_t stride = calc_plane_stride(fb, 0);
> >
> > We could return -EINVAL in case fb->num_planes != 1.
>
> Let's not waste cycles. With this ^ fixed, this patch is:
>
> Reviewed-by: Simon Ser <simon.ser@intel.com>
>
> Other nits are optional.

I agreed with all your suggestions, and I already applied all of them.
Should I wait for the other patches review, or should I resend the new
version?

Thanks for all the feedback
Best Regards

> > > + if (fb->is_dumb)
> > > + map = kmstest_dumb_map_buffer(fb->fd, fb->gem_handle, fb->size,
> > > + PROT_READ);
> > > + else
> > > + map = gem_mmap__gtt(fb->fd, fb->gem_handle, fb->size,
> > > + PROT_READ);
> > > + ptr = map;
> >
> > Nit: no need for this, can assign the result of mmap directly to ptr.
> >
> > > +
> > > + /*
> > > + * Framebuffers are often uncached, which can make byte-wise accesses
> > > + * very slow. We copy each line of the FB into a local buffer to speed
> > > + * up the hashing.
> > > + */
> > > + line = malloc(stride);
> > > + if (!line) {
> > > + munmap(map, fb->size);
> > > + return -ENOMEM;
> > > + }
> > > +
> > > + hash = FNV1a_OFFSET_BIAS;
> > > +
> > > + for (y = 0; y < fb->height; y++, ptr += stride) {
> > > +
> > > + igt_memcpy_from_wc(line, ptr, stride);
> >
> > Nit: no need to copy the whole stride actually, we can just copy
> > fb->width * cpp since we're only going to read that.
> >
> > > +
> > > + for (x = 0; x < fb->width * cpp; x++) {
> > > + hash ^= line[x];
> > > + hash *= FNV1a_PRIME;
> > > + }
> > > + }
> > > +
> > > + crc->n_words = 1;
> > > + crc->crc[0] = hash;
> > > +
> > > + free(line);
> > > + munmap(map, fb->size);
> > > +
> > > + return 0;
> > > +#undef FNV1a_OFFSET_BIAS
> > > +#undef FNV1a_PRIME
> > > +}
> > > +
> > > /**
> > > * igt_format_is_yuv:
> > > * @drm_format: drm fourcc
> > > diff --git a/lib/igt_fb.h b/lib/igt_fb.h
> > > index adefebe1..a2741c05 100644
> > > --- a/lib/igt_fb.h
> > > +++ b/lib/igt_fb.h
> > > @@ -37,6 +37,7 @@
> > > #include <i915_drm.h>
> > >
> > > #include "igt_color_encoding.h"
> > > +#include "igt_debugfs.h"
> > >
> > > /*
> > > * Internal format to denote a buffer compatible with pixman's
> > > @@ -194,5 +195,7 @@ int igt_format_plane_bpp(uint32_t drm_format, int plane);
> > > void igt_format_array_fill(uint32_t **formats_array, unsigned int *count,
> > > bool allow_yuv);
> > >
> > > +int igt_fb_get_crc(struct igt_fb *fb, igt_crc_t *crc);
> > > +
> > > #endif /* __IGT_FB_H__ */
> > >
> > > _______________________________________________
> > > igt-dev mailing list
> > > igt-dev@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/igt-dev
> > _______________________________________________
> > igt-dev mailing list
> > igt-dev@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/igt-dev

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Rodrigo Siqueira
https://siqueira.tech

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