On Fri, 27 Oct 2017 22:29:32 +0100, Ralph Corderoy said:
What does `scan -version' give? Is 1-10426 actually 10,426 emails? :-)
Linux-kernel is a firehose. 800 to 1200 emails a day (depending on whether or not Greg KH drops a -stable review patchbomb series, those can be 300 mails right there :). And I probably subscribed to the list around kernel 2.5.47 (Nov 2002), at which time it was still a garden hose :)
If you have grep(1) read the files up to the end of the headers instead, does it still take as long? Something like
(as root) echo 3 >| /proc/sys/vm/drop_caches to get cache-cold first run [~/Mail/linux-kernel] time grep -m1 '^$' `seq 1 10426` > /dev/null real 0m17.566s user 0m0.141s sys 0m2.087s [~/Mail/linux-kernel] time grep -m1 '^$' `seq 1 10426` > /dev/null real 0m0.187s user 0m0.052s sys 0m0.129s So cache-cold is within 0.5%. I'm pretty sure what we're measuring there is how many rotations at 5400rpm are needed (and given that on a cache-cold it will need at least 1 i/O to read the inode and get the extent list, and a second to read the first 4K of the file, that's 20,852 I/O minimum. And in 17.5 seconds there's only 94,500 rotations. And assuming a 1ms track-to-track seek time, each one eats the equivalent of 5 rotations, 4 if it's smart enough to do rotational positioning during the seek - which eats up the rest of the available rotations and then some unless we've got some read-ahead going.... (several tries later) Well, cache-cold time changed. Now is a consistent: time grep -m1 '^$' `seq 1 10426` > /dev/null real 0m10.781s Conclusion 1: The disk is known to be a hybrid (with a small 16G or so flash on the front), and after 4 or 5 references, they've been promoted to flash. Not sure that 10.7s makes sense, I would have expected more speedup. Conclusion 2: I don't understand ext4 as well as I thought I did. ;)
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