Re: newer /bin/cp have worse btrfs fiemap performance.

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

a fix.

> Hi,
> 
> newer /bin/cp have worse btrfs fiemap performance.
> 
> btrfs version: misc-next 750de989d367(the lastest of 2022/11/05)
> /bin/cp versions(run them on the same server)
>     8.22 copy from centos/7.9

this
>     8.30 rocklinux/9.0
should be
	8.30 rocklinux/8

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2022/11/06

>     9.1 local build, https://kojipkgs.fedoraproject.org/packages/coreutils/9.1/8.eln121/
> 
> test case:
>     /bin/cp /mnt/test/file1 /dev/null
>     /mnt/test/file1 is created by https://lore.kernel.org/linux-btrfs/YuwUw2JLKtIa9X+S@localhost.localdomain/T/#T
>     and /mnt/test/file1 is 256M.
> 
>     file is not cached: 'echo 3 >/proc/sys/vm/drop_caches'
>     file is cached: run '/bin/cp /mnt/test/file1 /dev/null' again.
> 
> performance result(/bin/cp /mnt/test/file1 /dev/null):
> /bin/cp 9.1
>     file is not cached: 94.85(1:34.85)
>     file is cached: 1982.43(33:02.43)
> /bin/cp 8.30
>     file is not cached: 1.48(0:01.48)
>     file is cached:14.07(0:14.07)
> /bin/cp 8.22
>     file is not cached: 0.53(0:00.53)
>     file is cached: 0.10(0:00.10)
> 
> as a compare, we test it on xfs too.
> 1) /bin/cp 8.22/8.30/9.1 have almost same performance.
> 2) the case(the file is cached) is faster than the case(the file is not
> cached).
> 
> strace show that the logical of /bin/cp 8.30 and 9.1 are different.
> /bin/cp 8.30
>     lseek(3, 198737920, SEEK_SET)           = 198737920
>     write(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     read(3, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     write(4, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     lseek(3, 198746112, SEEK_SET)           = 198746112
>     write(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     read(3, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     write(4, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
> 
> /bin/cp 9.1
>     lseek(3, 880640, SEEK_DATA)             = 884736
>     lseek(3, 884736, SEEK_HOLE)             = 888832
>     lseek(3, 884736, SEEK_SET)              = 884736
>     write(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     read(3, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     write(4, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     lseek(3, 888832, SEEK_DATA)             = 892928
>     lseek(3, 892928, SEEK_HOLE)             = 897024
>     lseek(3, 892928, SEEK_SET)              = 892928
>     write(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     read(3, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
>     write(4, "a\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4096
> 
> Do we need some job in btrfs to support /bin/cp 9.1 well,
> or /bin/cp 9.1 is just wrong?
> 
> Best Regards
> Wang Yugui (wangyugui@e16-tech.com)
> 2022/11/06
>