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Re: Slow read(2) and write(2) syscalls

On 29/04/2020 15:37, Sad Clouds wrote:
On Wed, 29 Apr 2020 09:17:54 +0100
Chavdar Ivanov <> wrote:

On my VirtualBox 6.1.6 guest running -current amd64 I get:

$  time cat 80mb > /dev/null
cat 80mb > /dev/null  0.00s user 0.02s system 98% cpu 0.021 total

dd if=/dev/zero of=out bs=1m count=10000

do you get similar I/O throughput on NetBSD and Linux guests?

Make sure you use the fdatasync option on linux when using dd for writing. Otherwise it just writes as much as it can to cache and then returns without actually waiting for the write to complete falsely inflating the performance.

I haven't tried with anything later than 7 but I use virtual box hosted on windows a lot with ahci storage emulation. In the last tests I did I was getting 100MB/s write performance with both Ubuntu (kernel 4.4) and NetBSD 7. For reference the underlying disk in that case was a 2TB ATA attached to an AHCI controller.

I can spin up a 9.x VM and test that relatively easily. current would take a little longer as I'd have to build it first :)


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