Thanks for your interest.
In practice, I haven't yet proven that any of my devices actually do benefit from a max GB/cdb greater than 0.000065536 while an fs is mounted ...
You mean, 64 KByte/request?
Probably yes. Sorry I don't know what a "request" is. Do you already know what a "cdb" is? In usbmassbulk_10.pdf notation, the cdb (aka CDB) is the bCBLength bytes of the bCBWCB.
I'm saying I see cdb's commonly choked off at a max of 64 KiB each in Windows, and I hear Matt D proposing, for the sake of broader interoperability, we copy that limit into Linux and make its workaround obscure. I'm saying that limit necessarily multiplies command + status overhead by exponentially increasing numbers as the size of the typical shattered stream grows exponentially with the passing of years.
I'm curious what the relevant number is for IDE or SATA... and how disk and page caching affect it.
Me too.
I hear part of the drive behind SATA command queueing is to work around the bytes/cdb chokehold in the host. I notice PCI ATA nominally forces the driver to preallocate and pin all the data of a cdb before beginning the cdb, yuck. For a max of 64 Ki - 1 blocks at 2 KiB/block that could be 128 MiB - 2 KiB.
Things like MKFS (and badblocks) certainly like to issue much bigger requests.
mkfs is rare?
man badblocks I will now enjoy, thank you.
If we make that easy for me to prove, then we will have created a volunteer to work towards making the whitelisting more automagic.
Assuming max_sectors is changeable through sysfs, the experiment would be just to measure elapsed time while doing various common tasks.
Yes.
There are lots of benchmarks available. There are lots of benchmarks available. There are lots of benchmarks available. There are lots of benchmarks available.
(: That bears repeating. :)
I don't know how to discover which benchmarks measure something real i.e. something that matters to people running apps other than benchmarks. linux-fsdevel has a list of benchmarks to try.
Without a credible argument to say bytes/cdb matters, I can't effectively argue with pointy-haired folk to help free more time/ people/ me to improve it.
Pat LaVarre
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