Hello. On 22-11-2010 2:35, Mark Lord wrote:
While working on something unrelated today, I instrumented ata_sff_data_xfer32() to generate a printk() on each invocation.
Imagine then my complete surprise to see that print() being invoked very frequently after rebooting with the modified kernel.
ata_sff_data_xfer32() is for PIO read/writes.. something that I don't expect to see.
This is an ata_piix system, with a pure SATA SSD.
Most PIO I/O you saw points to an ATAPI device...
Why are we using PIO so much? Or am I simply misunderstanding something basic here.. ?
Confused.
ata_sff_data_xfer32: buf=f68015fc:512 (write) ata1.00: ATA-8: OCZ-VERTEX, 1.6, max UDMA/133 ata1.00: 250069680 sectors, multi 1: LBA48 NCQ (depth 0/32) ata_sff_data_xfer32: buf=f6801f80:512 (write) ata1.00: configured for UDMA/133 scsi 0:0:0:0: Direct-Access ATA OCZ-VERTEX 1.6 PQ: 0 ANSI: 5 sd 0:0:0:0: Attached scsi generic sg0 type 0 sd 0:0:0:0: [sda] 250069680 512-byte logical blocks: (128 GB/119 GiB) sd 0:0:0:0: [sda] Write Protect is off sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00 sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA sda: sda1 sda2 sd 0:0:0:0: [sda] Attached SCSI disk ata_sff_data_xfer32: buf=f68055fc:512 (write) ata2.00: ATAPI: SlimtypeDVD A DS8A1P, CX16, max UDMA/33 ata_sff_data_xfer32: buf=f6805f80:512 (write) ata2.00: configured for UDMA/33 ata_sff_data_xfer32: buf=f68053a8:12 (read) ata_sff_data_xfer32: buf=f68040c4:12 (read) ata_sff_data_xfer32: buf=f7088e00:36 (write)
I think you have your (read)/(write) backwars. 12 bytes is the typical CDB length -- and CDB is written, not read. 36 bytes seems to be INQUIRY data length -- which is read, not written. 512 bytes then stand for IDENTIFY [PACKET] DEVICE data.
ata_sff_data_xfer32: buf=f68040c4:12 (read) scsi 1:0:0:0: CD-ROM Slimtype DVD A DS8A1P CX16 PQ: 0 ANSI: 5 ata_sff_data_xfer32: buf=f68040c4:12 (read) ata_sff_data_xfer32: buf=f68053a8:12 (read) ata_sff_data_xfer32: buf=f73b1580:18 (write)
This seems to be REQUEST SENSE command and (perhaps) TEST UNIT READY preceding it...
...
You're seeing so many PIO transfers because libata doesn't use DMA with ATAPI transfers which aren't divisible by sector size (this is a hardware limitation on many chips).
WBR, Sergei -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
