drm/i915: Cache the error string
Currently, we convert the error state into a string every time we read from sysfs (and sysfs reads in page size (4KiB) chunks). We do try to window the string and only capture the portion that is being read, but that means that we must always convert up to the window to find the start. For a very large error state bordering on EXEC_OBJECT_CAPTURE abuse, this is noticeable as it degrades to O(N^2)! As we do not have a convenient hook for sysfs open(), and we would like to keep the lazy conversion into a string, do the conversion of the whole string on the first read and keep the string until the error state is freed. v2: Don't double advance simple_read_from_buffer v3: Due to extreme pain of lack of vrealloc, use a scatterlist v4: Keep the forward iterator loosely cached v5: Stylistic improvements to reduce patch size Reported-by: Jason Ekstrand <jason@jlekstrand.net> Testcase: igt/gem_exec_capture/many* Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Cc: Jason Ekstrand <jason@jlekstrand.net> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20181123132325.26541-1-chris@chris-wilson.co.uk
Please register or sign in to comment