Hello, I've got a big box of audio CDs to read, so I hooked up a load of SATA CDROM drives to a machine (Intel motherboard AHCI, and SATA SiI3124 controllers - in this example one was attached to each host controller), so that I could read them in parallel. I'm using kernel 3.16.3, with cdparanoia 3.10.2 - both from Debian Jessie. https://www.xiph.org/paranoia/manual.html When two (or more) drives are read simultaneously, the performance falls to pieces (throughput from each drive drops by 95%) if more than one /dev/sr* device is being read by cdparanoia. If I tell cdparanoia to use the corresponding /dev/sg devices, then no significant throughput drop is experienced when reading multiple drives simultaneously. As an example, using these two drives: [1:0:0:0] cd/dvd TSSTcorp DVD+-RW TS-H653G DW10 /dev/sr0 /dev/sg4 [14:0:0:0] cd/dvd PLDS DVD+-RW DH-16A6S YD11 /dev/sr9 /dev/sg16 ... in the following results I used "time cdparanoia -v -d /dev/XXX 1 /tmp/1.wav" - where XXX was substituted for either sr9 or sg16 On an otherwise idle machine, I did these two sequentially: sr9: 38 seconds sg16: 38 seconds Simultaneous with: cdparanoia -d /dev/sr0 11 /tmp/11.wav (and auto restarted that command when it completed) I then ran these two sequentially: sr9: 680 seconds sg16: 38 seconds Simultaneous with: cdparanoia -d /dev/sg4 11 /tmp/11.wav as above: sr9: 40 seconds sg16: 40 seconds This is a diff of the two sets of cdparanoia -v output (using the sr devices vs the sg devices): --- /tmp/sr 2014-11-06 12:41:43.094867889 +0000 +++ /tmp/sg 2014-11-06 12:42:00.463123769 +0000 @@ -2,9 +2,9 @@ Using cdda library version: 10.2 Using paranoia library version: 10.2 -Checking /dev/sr9 for cdrom... - Testing /dev/sr9 for SCSI/MMC interface - SG_IO device: /dev/sr9 +Checking /dev/sg16 for cdrom... + Testing /dev/sg16 for SCSI/MMC interface + SG_IO device: /dev/sg16 CDROM model sensed sensed: PLDS DVD+-RW DH-16A6S YD11 @@ -13,9 +13,9 @@ Checking for MMC style command set... Drive is MMC style - DMA scatter/gather table entries: 1 + DMA scatter/gather table entries: 167 table entry size: 131072 bytes - maximum theoretical transfer: 55 sectors + maximum theoretical transfer: 9185 sectors Setting default read size to 27 sectors (63504 bytes). Verifying CDDA command set... @@ -23,3 +23,5 @@ I'm happy to try other kernel versions to gather more data. Which kernel trees/branches should I try? I'm also assuming this is more likely to be a SCSI layer bug than a SATA one, so let me know if that's probably wrong. Also, is reporting here best or bugzilla? Cheers, Tim. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
