Re: [gentoo-user] Slightly OT - My new SSD.

[Adam Carter]

> That, indeed, seems to to be the case.  When I do cat /proc/interrupts |
> egrep '(CPU/nvm)', I get just the header line with one data line:
>
>            CPU0       CPU1       CPU2       CPU3
>  17:          0          0         15      14605   IO-APIC 17-fasteoi
>  ehci_hcd:usb1, nvme0q0, nvme0q1
>
> I'm kind of feeling a bit out of my depth here.  What are the nvme0q0,
> etc.?  "Queues" of some kind?  You appear to have nine of these things,
> I've just got two.  I'm sure there's a fine manual I ought to be
> reading.  Do you know where I might find this manual?
>

Can't remember where i read up on this. Might have been troubleshooting
poor small packet performance on a firewall (some network drivers can have
multiqueue too). Maybe start with this;
https://www.thomas-krenn.com/en/wiki/Linux_Multi-Queue_Block_IO_Queueing_Mechanism_(blk-mq)

It looks like the nvme driver was made "mutliqueue" in kernel 3.19.

FWIW my system is 8 core (AMD 8350). Its odd having two queues on the same
interrupt, but I have the same for q0 and q1, but on your system i'd say
there should be some queues on other interrupts to they can be serviced by
other cores, so that doesnt look right.

Do you have MSI enabled? Bus options -> PCI Support -> Message Signaled
Interrupts (MSI and MSI-X)
If your system is not too old you may get more interrupts or a better
spread with that enabled.

When I look at the entire /proc/interrupts, there are just 30 lines
> listed, and I suspect there are no more than 32 interrupt numbers
> available.  Is there any way I can configure Linux to give my SSD more
> than one interrupt line to work with?
>
> > FWIW
> > # hdparm -tT /dev/nvme0n1
>
> > /dev/nvme0n1:
> >  Timing cached reads:   9884 MB in  2.00 seconds = 4945.35 MB/sec
> >  Timing buffered disk reads: 4506 MB in  3.00 seconds = 1501.84 MB/sec
>
> I get:
>
> /dev/nvme0n1:
>  Timing cached reads:   4248 MB in  2.00 seconds = 2124.01 MB/sec
>  Timing buffered disk reads: 1214 MB in  3.00 seconds = 404.51 MB/sec
>
> So my "cached reads" speed is (a little under) half of yours.  This is
> to be expected, since my PCIe lanes are only version 2 (and yours are
> probably version 3).


FWIW the motherboard manual says it has PCIe 2.0 x16 slots. Agree that
cache speed is likely a hardware issue.


> But the "buffered disk read" are much slower.  Is
> this just the age of my PC, or might I have something suboptimally
> configured?
>

You look like you're getting SATA speeds, but since you have the nvme
device, i guess that implies you havent fallen back to SATA. Could well be
older hardware or less PCIe slots/lanes.