Re: [PATCH] btrfs-progs: align btrfs receive buffer to enable fast CRC

[Sheng Mao <shngmao@gmail.com>]

Alignment to cache line is a great idea. I guess compiler can issue
faster memcpy version.

Thank you!

On Wed, Jan 06, 2021 at 01:16:35PM +0100, David Sterba wrote:
> 
> On Sat, Dec 26, 2020 at 02:46:06PM -0700, shngmao@gmail.com wrote:
> > From: Sheng Mao <shngmao@gmail.com>
> > 
> > To use optimized CRC implemention, the input buffer must be
> > unsigned long aligned. btrfs receive calculates checksum based on
> > read_buf, including btrfs_cmd_header (with zero-ed CRC field)
> > and command content. GCC attribute is added to both struct
> > btrfs_send_stream and read_buf to make sure read_buf is allocated
> > with proper alignment.
> > 
> > Issue: #324
> 
> The issue has a lot of interesting debugging and performance information
> so I'd put something to the changelog as well.
> 
> The alignment fixup sounds correct, though I'd push it a bit further and
> move read_buf to the beginning of the structure and align the whole
> structure to 64 bytes, as this is the common cache line size. This could
> potentially help too with memcpy.