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The IO performance test with fio after removing the likely and unlikely macros in all if-statement shows no performance drop. They do not help for the performance of rnbd. The fio test did random read on 32 rnbd devices and 64 processes. Test environment: - AMD Opteron(tm) Processor 6386 SE - 125G memory - kernel version: 5.4.86 - gcc version: gcc (Debian 8.3.0-6) 8.3.0 - Infiniband controller: InfiniBand: Mellanox Technologies MT26428 [ConnectX VPI PCIe 2.0 5GT/s - IB QDR / 10GigE] (rev b0) before read: IOPS=549k, BW=2146MiB/s read: IOPS=544k, BW=2125MiB/s read: IOPS=553k, BW=2158MiB/s read: IOPS=535k, BW=2089MiB/s read: IOPS=543k, BW=2122MiB/s read: IOPS=552k, BW=2154MiB/s average: IOPS=546k, BW=2132MiB/s after read: IOPS=556k, BW=2172MiB/s read: IOPS=561k, BW=2191MiB/s read: IOPS=552k, BW=2156MiB/s read: IOPS=551k, BW=2154MiB/s read: IOPS=562k, BW=2194MiB/s ----------- average: IOPS=556k, BW=2173MiB/s The IOPS and bandwidth got better slightly after removing likely/unlikely. (IOPS= +1.8% BW= +1.9%) But we cannot make sure that removing the likely/unlikely help the performance because it depends on various situations. We only make sure that removing the likely/unlikely does not drop the performance. Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com> Reviewed-by: Md Haris Iqbal <haris.iqbal@ionos.com> Link: https://lore.kernel.org/r/20210428061359.206794-5-gi-oh.kim@ionos.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.