> Hi, > > On 26 April 2017 at 21:19, Bryan Gurney <bgurney@xxxxxxxxxxxx> wrote: > > > > I performed some tests for various non-zero values of > > "buffer_compress_percentage", and the resulting data was not dedupable > > (which would be consistent with the behavior of "scramble_buffers=1", > > but > > the data pattern seems to suggest that the algorithm used in > > scramble_buffers is not being used. Comparing this to when > > buffer_compress_percentage is set to zero, the resulting data is almost > > incompressible, but exhibits a high frequency of dedupe. This is > > despite > > the intentions of the user's configuration for buffer data content of 0% > > compression, and scrambled to avoid dedupe. > > http://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-buffer-compress-percentage > alludes to buffer_compress_percentage=0 actually turning the option > off rather than setting a compression ratio of 0%. Here's a link to > the code that would normally react to the option: > https://github.com/axboe/fio/blob/fio-2.19/io_u.c#L2045 . > > -- > Sitsofe | http://sucs.org/~sits/ > Hi Sitsofe, Thanks, I actually didn't know about that part in fill_io_buffer(), which ultimately disables compression by the nature of the buffer_compress_percentage value being 0. However, the part that caught my attention was also in io_u.c, inside the function "struct io_u *get_io_u(struct thread_data *td)", starting here: https://github.com/axboe/fio/blob/fio-2.19/io_u.c#L1644 if (io_u->ddir == DDIR_WRITE) { if (td->flags & TD_F_REFILL_BUFFERS) { io_u_fill_buffer(td, io_u, td->o.min_bs[DDIR_WRITE], io_u->buflen); } else if ((td->flags & TD_F_SCRAMBLE_BUFFERS) && !(td->flags & TD_F_COMPRESS)) do_scramble = 1; if (td->flags & TD_F_VER_NONE) { populate_verify_io_u(td, io_u); do_scramble = 0; } } else if (io_u->ddir == DDIR_READ) { ... Note that "do_scramble" is only set to 1 if (td->flags & TD_F_SCRAMBLE_BUFFERS) is true, AND (td->flags & TD_F_COMPRESS) is false. If I'm reading this correctly, the TD_F_ flags indicate whether the specified option was passed to fio by the user or script. Thanks, Bryan -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
