Re: [PATCHSET v6 0/12] Uncached buffered IO

Jens Axboe
2024-12-12T15:46:44Z

On 12/10/24 2:48 AM, Bharata B Rao wrote:
> Hi Jens,
>
> I ran a couple of variants of FIO to check how this patchset affects the
> FIO numbers. My other motivation with this patchset is to check if it
> improves the scalability issues that were discussed in [1] and [2].
> But for now, here are some initial numbers.

Thanks for testing!

> Also note that I am using your buffered-uncached.8 branch from
> https://git.kernel.dk/cgit/linux/log/?h=buffered-uncached.8 that has
> changes to enable uncached buffered IO for EXT4 and block devices.
>
> In the below reported numbers,
> 'base' means kernel from buffered-uncached.8 branch and
> 'patched' means kernel from buffered-uncached.8 branch + above shown FIO change
>
> FIO on EXT4 partitions
> ======================
> nvme1n1 259:12 0 3.5T 0 disk
> ??nvme1n1p1 259:13 0 894.3G 0 part /mnt1
> ??nvme1n1p2 259:14 0 894.3G 0 part /mnt2
> ??nvme1n1p3 259:15 0 894.3G 0 part /mnt3
> ??nvme1n1p4 259:16 0 894.1G 0 part /mnt4
>
> fio -directory=/mnt4/ -direct=0 -thread -size=3G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
> fio -directory=/mnt3/ -direct=0 -thread -size=3G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
> fio -directory=/mnt1/ -direct=0 -thread -size=3G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
> fio -directory=/mnt2/ -direct=0 -thread -size=3G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
>
> Four NVME devices are formatted with EXT4 and four parallel FIO instances
> are run on them with the options as shown above.
>
> FIO output looks like this:
>
> base:
> READ: bw=1233MiB/s (1293MB/s), 1233MiB/s-1233MiB/s (1293MB/s-1293MB/s), io=4335GiB (4654GB), run=3600097-3600097msec
> WRITE: bw=529MiB/s (554MB/s), 529MiB/s-529MiB/s (554MB/s-554MB/s), io=1858GiB (1995GB), run=3600097-3600097msec
> READ: bw=1248MiB/s (1308MB/s), 1248MiB/s-1248MiB/s (1308MB/s-1308MB/s), io=4387GiB (4710GB), run=3600091-3600091msec
> WRITE: bw=535MiB/s (561MB/s), 535MiB/s-535MiB/s (561MB/s-561MB/s), io=1880GiB (2019GB), run=3600091-3600091msec
> READ: bw=1235MiB/s (1294MB/s), 1235MiB/s-1235MiB/s (1294MB/s-1294MB/s), io=4340GiB (4660GB), run=3600094-3600094msec
> WRITE: bw=529MiB/s (555MB/s), 529MiB/s-529MiB/s (555MB/s-555MB/s), io=1860GiB (1997GB), run=3600094-3600094msec
> READ: bw=1234MiB/s (1294MB/s), 1234MiB/s-1234MiB/s (1294MB/s-1294MB/s), io=4337GiB (4657GB), run=3600093-3600093msec
> WRITE: bw=529MiB/s (554MB/s), 529MiB/s-529MiB/s (554MB/s-554MB/s), io=1859GiB (1996GB), run=3600093-3600093msec
>
> patched:
> READ: bw=1400MiB/s (1469MB/s), 1400MiB/s-1400MiB/s (1469MB/s-1469MB/s), io=4924GiB (5287GB), run=3600100-3600100msec
> WRITE: bw=600MiB/s (629MB/s), 600MiB/s-600MiB/s (629MB/s-629MB/s), io=2110GiB (2266GB), run=3600100-3600100msec
> READ: bw=1395MiB/s (1463MB/s), 1395MiB/s-1395MiB/s (1463MB/s-1463MB/s), io=4904GiB (5266GB), run=3600148-3600148msec
> WRITE: bw=598MiB/s (627MB/s), 598MiB/s-598MiB/s (627MB/s-627MB/s), io=2102GiB (2257GB), run=3600148-3600148msec
> READ: bw=1385MiB/s (1452MB/s), 1385MiB/s-1385MiB/s (1452MB/s-1452MB/s), io=4868GiB (5227GB), run=3600136-3600136msec
> WRITE: bw=594MiB/s (622MB/s), 594MiB/s-594MiB/s (622MB/s-622MB/s), io=2087GiB (2241GB), run=3600136-3600136msec
> READ: bw=1376MiB/s (1443MB/s), 1376MiB/s-1376MiB/s (1443MB/s-1443MB/s), io=4837GiB (5194GB), run=3600145-3600145msec
> WRITE: bw=590MiB/s (618MB/s), 590MiB/s-590MiB/s (618MB/s-618MB/s), io=2073GiB (2226GB), run=3600145-3600145msec
>
> FIO on block devices
> ====================
> nvme1n1 259:12 0 3.5T 0 disk
> ??nvme1n1p1 259:13 0 894.3G 0 part
> ??nvme1n1p2 259:14 0 894.3G 0 part
> ??nvme1n1p3 259:15 0 894.3G 0 part
> ??nvme1n1p4 259:16 0 894.1G 0 part
>
> fio -filename=/dev/nvme1n1p4 -direct=0 -thread -size=800G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
> fio -filename=/dev/nvme1n1p2 -direct=0 -thread -size=800G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
> fio -filename=/dev/nvme1n1p1 -direct=0 -thread -size=800G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
> fio -filename=/dev/nvme1n1p3 -direct=0 -thread -size=800G -rw=rw -rwmixwrite=30 --norandommap --randrepeat=0 -ioengine=pvsync2 -bs=64k -numjobs=252 -runtime=3600 --time_based -group_reporting -name=mytest
>
> Four instances of FIO are run on four different NVME block devices
> with the options as shown above.
>
> base:
> READ: bw=8712MiB/s (9135MB/s), 8712MiB/s-8712MiB/s (9135MB/s-9135MB/s), io=29.9TiB (32.9TB), run=3600011-3600011msec
> WRITE: bw=3734MiB/s (3915MB/s), 3734MiB/s-3734MiB/s (3915MB/s-3915MB/s), io=12.8TiB (14.1TB), run=3600011-3600011msec
> READ: bw=8727MiB/s (9151MB/s), 8727MiB/s-8727MiB/s (9151MB/s-9151MB/s), io=30.0TiB (32.9TB), run=3600005-3600005msec
> WRITE: bw=3740MiB/s (3922MB/s), 3740MiB/s-3740MiB/s (3922MB/s-3922MB/s), io=12.8TiB (14.1TB), run=3600005-3600005msec
> READ: bw=8701MiB/s (9123MB/s), 8701MiB/s-8701MiB/s (9123MB/s-9123MB/s), io=29.9TiB (32.8TB), run=3600004-3600004msec
> WRITE: bw=3729MiB/s (3910MB/s), 3729MiB/s-3729MiB/s (3910MB/s-3910MB/s), io=12.8TiB (14.1TB), run=3600004-3600004msec
> READ: bw=8706MiB/s (9128MB/s), 8706MiB/s-8706MiB/s (9128MB/s-9128MB/s), io=29.9TiB (32.9TB), run=3600005-3600005msec
> WRITE: bw=3731MiB/s (3913MB/s), 3731MiB/s-3731MiB/s (3913MB/s-3913MB/s), io=12.8TiB (14.1TB), run=3600005-3600005msec
>
> patched:
> READ: bw=1844MiB/s (1933MB/s), 1844MiB/s-1844MiB/s (1933MB/s-1933MB/s), io=6500GiB (6980GB), run=3610641-3610641msec
> WRITE: bw=790MiB/s (828MB/s), 790MiB/s-790MiB/s (828MB/s-828MB/s), io=2786GiB (2991GB), run=3610642-3610642msec
> READ: bw=1753MiB/s (1838MB/s), 1753MiB/s-1753MiB/s (1838MB/s-1838MB/s), io=6235GiB (6695GB), run=3641973-3641973msec
> WRITE: bw=751MiB/s (788MB/s), 751MiB/s-751MiB/s (788MB/s-788MB/s), io=2672GiB (2869GB), run=3641969-3641969msec
> READ: bw=1078MiB/s (1130MB/s), 1078MiB/s-1078MiB/s (1130MB/s-1130MB/s), io=3788GiB (4068GB), run=3600007-3600007msec
> WRITE: bw=462MiB/s (484MB/s), 462MiB/s-462MiB/s (484MB/s-484MB/s), io=1624GiB (1743GB), run=3600007-3600007msec
> READ: bw=1752MiB/s (1838MB/s), 1752MiB/s-1752MiB/s (1838MB/s-1838MB/s), io=6234GiB (6694GB), run=3642657-3642657msec
> WRITE: bw=751MiB/s (788MB/s), 751MiB/s-751MiB/s (788MB/s-788MB/s), io=2672GiB (2869GB), run=3642622-3642622msec
>
> While FIO on FS shows improvement, FIO on block shows numbers going down.
> Is this expected or am I missing enabling anything else for the block option?

The fs side looks as expected, that's a nice win. For the bdev side, I
deliberately did not post the bdev patch for enabling uncached buffered
IO on a raw block device, as it's just a hack for testing. It currently
needs punting similar to dirtying of pages, and it's not optimized at
all. We really need the raw bdev ops moving fully to iomap and not being
dependent on buffer_heads for this to pan out, so the most likely
outcome here is that raw bdev uncached buffered IO will not really be
supported until the time that someone (probably Christoph) does that
work.

I don't think this is a big issue, can't imagine buffered IO on raw
block devices being THAT interesting of a use case.

--
Jens Axboe