Re: [Intel-gfx] [PATCH] drivers/gpu/drm/i915/selftests/i915_buddy.c: Fix bug
Quoting George Spelvin (2020-03-25 19:24:29) > igt_mm_config() calls ilog2() on the (pseudo)random 21-bit number > s>>12. Once in 2 million seeds, this is zero and ilog2 summons > the nasal demons. I ran into a similar bug with random returning 0 and remembered this patch sitting around. Pushed, and many thanks for the fix! -Chris ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
Re: [Intel-gfx] [PATCH] drivers/gpu/drm/i915/selftests/i915_buddy.c: Fix bug
On Thu, 26 Mar 2020 at 20:21, George Spelvin wrote: > > On Thu, Mar 26, 2020 at 05:04:43PM +, Matthew Auld wrote: > > Reviewed-by: Matthew Auld > > Thank you! I got some incomprehensible error emails (reproduced at > https://patchwork.freedesktop.org/series/75090/) from the patchwork > daemon, complaining about additional test failures. Obviously, I care, > but I can't tell if this is a genuine error, or just a flaky test being > sensitive to the exact random number generation algorithm. > > If you understand these messages, do they look like I broke something? No, doesn't seem to be related to your change. https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_17090/shards-all.html?testfilter=buddy ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
Re: [Intel-gfx] [PATCH] drivers/gpu/drm/i915/selftests/i915_buddy.c: Fix bug
On Thu, Mar 26, 2020 at 05:04:43PM +, Matthew Auld wrote: > Reviewed-by: Matthew Auld Thank you! I got some incomprehensible error emails (reproduced at https://patchwork.freedesktop.org/series/75090/) from the patchwork daemon, complaining about additional test failures. Obviously, I care, but I can't tell if this is a genuine error, or just a flaky test being sensitive to the exact random number generation algorithm. If you understand these messages, do they look like I broke something? ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
Re: [Intel-gfx] [PATCH] drivers/gpu/drm/i915/selftests/i915_buddy.c: Fix bug
On Wed, 25 Mar 2020 at 21:23, George Spelvin wrote: > > igt_mm_config() calls ilog2() on the (pseudo)random 21-bit number > s>>12. Once in 2 million seeds, this is zero and ilog2 summons > the nasal demons. > > There was an attempt to handle this case with a max(), but that's > too late; ms could already be something bizarre. > > Given that the low 12 bits of s and ms are always zero, it's a lot > simpler just to divide them by 4096, then everything fits into 32 > bits, and we can easily generate a random number 1 <= s <= 0x1f. > > Signed-off-by: George Spelvin > Fixes: 14d1b9a6247c > Cc: Matthew Auld > Cc: Jani Nikula > Cc: Joonas Lahtinen > Cc: Rodrigo Vivi > Cc: intel-gfx@lists.freedesktop.org Reviewed-by: Matthew Auld ___ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
[Intel-gfx] [PATCH] drivers/gpu/drm/i915/selftests/i915_buddy.c: Fix bug
igt_mm_config() calls ilog2() on the (pseudo)random 21-bit number
s>>12. Once in 2 million seeds, this is zero and ilog2 summons
the nasal demons.
There was an attempt to handle this case with a max(), but that's
too late; ms could already be something bizarre.
Given that the low 12 bits of s and ms are always zero, it's a lot
simpler just to divide them by 4096, then everything fits into 32
bits, and we can easily generate a random number 1 <= s <= 0x1f.
Signed-off-by: George Spelvin
Fixes: 14d1b9a6247c
Cc: Matthew Auld
Cc: Jani Nikula
Cc: Joonas Lahtinen
Cc: Rodrigo Vivi
Cc: intel-gfx@lists.freedesktop.org
---
drivers/gpu/drm/i915/selftests/i915_buddy.c | 18 ++
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/i915/selftests/i915_buddy.c
b/drivers/gpu/drm/i915/selftests/i915_buddy.c
index 1b856bae67b53..b5d29dda45ddb 100644
--- a/drivers/gpu/drm/i915/selftests/i915_buddy.c
+++ b/drivers/gpu/drm/i915/selftests/i915_buddy.c
@@ -8,8 +8,6 @@
#include "../i915_selftest.h"
#include "i915_random.h"
-#define SZ_8G (1ULL << 33)
-
static void __igt_dump_block(struct i915_buddy_mm *mm,
struct i915_buddy_block *block,
bool buddy)
@@ -281,18 +279,22 @@ static int igt_check_mm(struct i915_buddy_mm *mm)
static void igt_mm_config(u64 *size, u64 *chunk_size)
{
I915_RND_STATE(prng);
- u64 s, ms;
+ u32 s, ms;
/* Nothing fancy, just try to get an interesting bit pattern */
prandom_seed_state(, i915_selftest.random_seed);
- s = i915_prandom_u64_state() & (SZ_8G - 1);
- ms = BIT_ULL(12 + (prandom_u32_state() % ilog2(s >> 12)));
- s = max(s & -ms, ms);
+ /* Let size be a random number of pages up to 8 GB (2M pages) */
+ s = 1 + i915_prandom_u32_max_state((1 << (33-12)) - 1, );
+ /* Let the chunk size be a random power of 2 less than size */
+ ms = (u32)1 << i915_prandom_u32_max_state(ilog2(s), );
+ /* Round size down to the chunk size */
+ s &= -ms;
- *chunk_size = ms;
- *size = s;
+ /* Convert from pages to bytes */
+ *chunk_size = (u64)ms << 12;
+ *size = (u64)s << 12;
}
static int igt_buddy_alloc_smoke(void *arg)
--
2.26.0
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