DragonFly users List (threaded) for 2011-04
Re: Recent concurrency improvements in the AHCI driver and CAM need testing
io_acpi => io_apic
On Sun, Apr 10, 2011 at 11:37 PM, Naoya Sugioka <email@example.com> wrote:
> This is happened before your recent update, but my laptop showing
> CMD=15; timeout
> on ahci0.1 when io_acpi is enabled. This timeout prevents to complete
> bootstrap process.
> I just wonder this is happened because ahci.0.1 is associated to ATAPI
> (DVD-RW) drive without
> dmesg telles:
> ahci0.1: Found ATAPI "TSSTcorp DVD+/-RW TS-U633F D200" serial="R3476GSSA81272"
> ahci0.1: tags=0/32 satacap=0202 satafea=0068 NCQ=NO capacity=1.00MB
> ahci0.1: f85=0000 f86=0000 f87=4000 WC=notsupp RA=notsupp SEC=notsupp
> then start showing a timeout message.
> Let me know if you need further information, thank you.
> On Sat, Apr 9, 2011 at 9:00 PM, Matthew Dillon
> <firstname.lastname@example.org> wrote:
>> I've pushed some serious changes to the AHCI SATA driver and CAM.
>> One fixes issues where the tags were not being utilized to their fullest
>> extent... well, really they weren't being utilized at all. I'm not
>> sure how I missed the problem before, but it is fixed now.
>> The second ensures that read requests cannot saturate all available
>> tags and cause writes to stall, and vise-versa, and also separates
>> out the read and write BIO streams and treats them as separate entities,
>> which means that reads can continue to be dispatched even if writes
>> saturate the drive's cache and writes can continue to be dispatched
>> even if concurrent read(s) would otherwise eat all available tags.
>> The reason the read/write saturation fixes are important is because
>> writes are usually completed instantly since they just go to the drive
>> cache, so even if reads are saturated there's no reason not to push
>> writes to the drive. Plus when the HD's cache becomes saturated writes
>> no longer complete instantly and would prevent reads from being
>> dispatched if all the tags were used to hold the writes.
>> With these fixes I am getting much better numbers with concurrency
>> I now get around 37000 IOPS doing random 512-byte sector reads with
>> a Crucial C300 SSD, verses ~8000 or so before the fix.
>> And I now get around ~365 IOPS with the same test on a hard drive,
>> verses ~150 IOPS before (remember these are random reads!).
>> blogbench also appears to have much better write/read parallelism
>> against the swapcache with the SSD/HD combo. Memory caches blow
>> out at around blog #1300 on my test boxes.
>> With the changes blogbench write performance is maintained through
>> blog #1600 or so, without the changes it drops off at #1300.
>> With the changes the swapcache SSD is pushing ~1400 IOPS or so
>> satisfying random read requests. Without the changes the swapcache
>> SSD is only pushing ~130 IOPS.
>> With the changes blogbench is able to maintain a ~60000 article
>> read rate at the end of the test. Without the changes the
>> read rate is more around ~10000 at the end of the test. At this
>> stage swapcache has cached a significant chunk of the data
>> in the SSD so the I/O activity is mixed random SSD and HD reads.
>> Ok, so I feel a bit sheepish that I missed the fact that the AHCI
>> driver wasn't utilizing its tags properly before. The difference
>> in performance is phenominal. Maybe we will start winning some
>> of those I/O benchmark tests now.
>> Matthew Dillon