On Wed, Apr 08, 2020 at 04:42:01PM -0700, Ashutosh Dixit wrote: > It is wrong to block the user thread in the next poll when OA data is > already available which could not fit in the user buffer provided in > the previous read. In several cases the exact user buffer size is not > known. Blocking user space in poll can lead to data loss when the > buffer size used is smaller than the available data. > > This change fixes this issue and allows user space to read all OA data > even when using a buffer size smaller than the available data using > multiple non-blocking reads rather than staying blocked in poll till > the next timer interrupt.
Thanks for providing this. Pushed to drm-intel-fixes targeting -rc2 > > v2: Fix ret value for blocking reads (Umesh) > v3: Mistake during patch send (Ashutosh) > v4: Remove -EAGAIN from comment (Umesh) > v5: Improve condition for clearing pollin and return (Lionel) > v6: Improve blocking read loop and other cleanups (Lionel) > v7: Added Cc stable > > Testcase: igt/perf/polling-small-buf > Reviewed-by: Lionel Landwerlin <lionel.g.landwer...@intel.com> > Signed-off-by: Ashutosh Dixit <ashutosh.di...@intel.com> > Cc: Umesh Nerlige Ramappa <umesh.nerlige.rama...@intel.com> > Cc: <sta...@vger.kernel.org> > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> > Link: > https://patchwork.freedesktop.org/patch/msgid/20200403010120.3067-1-ashutosh.di...@intel.com > --- > drivers/gpu/drm/i915/i915_perf.c | 65 ++++++-------------------------- > 1 file changed, 11 insertions(+), 54 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_perf.c > b/drivers/gpu/drm/i915/i915_perf.c > index 551be589d6f4..66a46e41d5ef 100644 > --- a/drivers/gpu/drm/i915/i915_perf.c > +++ b/drivers/gpu/drm/i915/i915_perf.c > @@ -2940,49 +2940,6 @@ void i915_oa_init_reg_state(const struct intel_context > *ce, > gen8_update_reg_state_unlocked(ce, stream); > } > > -/** > - * i915_perf_read_locked - &i915_perf_stream_ops->read with error > normalisation > - * @stream: An i915 perf stream > - * @file: An i915 perf stream file > - * @buf: destination buffer given by userspace > - * @count: the number of bytes userspace wants to read > - * @ppos: (inout) file seek position (unused) > - * > - * Besides wrapping &i915_perf_stream_ops->read this provides a common place > to > - * ensure that if we've successfully copied any data then reporting that > takes > - * precedence over any internal error status, so the data isn't lost. > - * > - * For example ret will be -ENOSPC whenever there is more buffered data than > - * can be copied to userspace, but that's only interesting if we weren't able > - * to copy some data because it implies the userspace buffer is too small to > - * receive a single record (and we never split records). > - * > - * Another case with ret == -EFAULT is more of a grey area since it would > seem > - * like bad form for userspace to ask us to overrun its buffer, but the user > - * knows best: > - * > - * http://yarchive.net/comp/linux/partial_reads_writes.html > - * > - * Returns: The number of bytes copied or a negative error code on failure. > - */ > -static ssize_t i915_perf_read_locked(struct i915_perf_stream *stream, > - struct file *file, > - char __user *buf, > - size_t count, > - loff_t *ppos) > -{ > - /* Note we keep the offset (aka bytes read) separate from any > - * error status so that the final check for whether we return > - * the bytes read with a higher precedence than any error (see > - * comment below) doesn't need to be handled/duplicated in > - * stream->ops->read() implementations. > - */ > - size_t offset = 0; > - int ret = stream->ops->read(stream, buf, count, &offset); > - > - return offset ?: (ret ?: -EAGAIN); > -} > - > /** > * i915_perf_read - handles read() FOP for i915 perf stream FDs > * @file: An i915 perf stream file > @@ -3008,7 +2965,8 @@ static ssize_t i915_perf_read(struct file *file, > { > struct i915_perf_stream *stream = file->private_data; > struct i915_perf *perf = stream->perf; > - ssize_t ret; > + size_t offset = 0; > + int ret; > > /* To ensure it's handled consistently we simply treat all reads of a > * disabled stream as an error. In particular it might otherwise lead > @@ -3031,13 +2989,12 @@ static ssize_t i915_perf_read(struct file *file, > return ret; > > mutex_lock(&perf->lock); > - ret = i915_perf_read_locked(stream, file, > - buf, count, ppos); > + ret = stream->ops->read(stream, buf, count, &offset); > mutex_unlock(&perf->lock); > - } while (ret == -EAGAIN); > + } while (!offset && !ret); > } else { > mutex_lock(&perf->lock); > - ret = i915_perf_read_locked(stream, file, buf, count, ppos); > + ret = stream->ops->read(stream, buf, count, &offset); > mutex_unlock(&perf->lock); > } > > @@ -3048,15 +3005,15 @@ static ssize_t i915_perf_read(struct file *file, > * and read() returning -EAGAIN. Clearing the oa.pollin state here > * effectively ensures we back off until the next hrtimer callback > * before reporting another EPOLLIN event. > + * The exception to this is if ops->read() returned -ENOSPC which means > + * that more OA data is available than could fit in the user provided > + * buffer. In this case we want the next poll() call to not block. > */ > - if (ret >= 0 || ret == -EAGAIN) { > - /* Maybe make ->pollin per-stream state if we support multiple > - * concurrent streams in the future. > - */ > + if (ret != -ENOSPC) > stream->pollin = false; > - } > > - return ret; > + /* Possible values for ret are 0, -EFAULT, -ENOSPC, -EIO, ... */ > + return offset ?: (ret ?: -EAGAIN); > } > > static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer *hrtimer) > -- > 2.25.2 > _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
