Mkfile(8) is severely syscall limited on OS X

Re:Mkfile(8) is severely syscall limited on OS X by fulafel on Sunday February 12, 2017 @08:41AM (#13628263)

It's just OS X being slow, Linux gets close to peak with a 16 kB buffer: http://blog.tdg5.com/tuning-dd-block-size/

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Re:Mkfile(8) is severely syscall limited on OS X by alain94040 on Sunday February 12, 2017 @11:41AM (#13629094)

Reading from /dev/zero and writing out to RAM with a more optimal block size of 256K yields a throughput of 1,536 MB/s

Actually, in this article, Linux writing to RAM is slower than MacOS writing to SSD. Hard to conclude that "it's just OS X being slow". I suspect the hardware used is wildly different from the one in the original article.

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Re:Mkfile(8) is severely syscall limited on OS X by mpweiher on Sunday February 12, 2017 @10:11AM (#13628658)

Maybe I am reading it wrong, but I am not getting the 16KB optimal buffer size from that article. The summary at the end is as follows:

'In the above example it can be seen that an input block size of 128K is optimal for my particular setup.'

However, the SSD seems to be significantly slower, so the relative overhead of the syscall is going to be respectively less:

'Reading from /dev/zero and writing out to a SSD with a more optimal block size of 256K yields a throughput of 280 MB/s.'

I was getting 250MB/s with the 512 byte buffer size, although the test in the article is doing two syscalls (one read(), one write()) whereas mkfile is just doing one.

At 256KB buffer size I was already getting around 1.8GB/second writing to SSD.

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Re:Mkfile(8) is severely syscall limited on OS X by feld on Sunday February 12, 2017 @11:22AM (#13629001)

Or is it another case of Linux taking shortcuts and sacrificing safety for speed?

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