On 09/28/2009 03:05 PM, Mike Christie wrote: > On 09/25/2009 05:19 PM, Vasu Dev wrote: >> Sometime max IO retries exhausts under heavy stress with >> large size IOs (>512K) and that leads to following IO errors. >> >> [ 2522.907984] sd 3:0:2:50: [sdu] Unhandled error code >> [ 2522.907990] sd 3:0:2:50: [sdu] Result: hostbyte=DID_ERROR >> driverbyte=DRIVER_OK >> [ 2522.907995] sd 3:0:2:50: [sdu] CDB: Write(10): 2a 00 00 00 08 00 00 >> 04 00 00 >> [ 2522.908012] end_request: I/O error, dev sdu, sector 2048 >> >> The FCoE stack doesn't have any direct flow control to fcoe stack >> for congestion due to temporary condition of longer link pauses >> or end-to-end delay between I-T-L, in turn under large IOs stress >> test sometimes max SCSI IO retries exhausts and leads to above IO >> errors and thrash of several retry attempts. >> >> Currently stack is configured with .sg_tablesize as SG_ALL (128) >> and that limits large IO up to 512K, so this patch reduces this >> to 64 to reduce cost of retrying on any failed large IO as this >> will limit large IOs to only upto 256K max. > > You probably get 256K with 64 sgs because you get lots of pages that are > not mergable. > > With sg_tablesize = 128 and ENABLE_CLUSTERING set, you can get a IO with > 128 * 64K. With 64 you can get 64 * 64K. 64K is the default max segment > size set by the block layer when a request_queue is created but > overridable in your sht->slave_configure callout. > > If you want to limit the IO size you want to set the max_sectors setting. > > Also you do not have to set max_sectors in the sht. You can do it from > userspace in /sys/block/sdX/queue. There is a hw max and max sectors.
Oops. You can set max sectors (the FS/BLOCK limit) in sysfs in the queue dir. You cannot set the max hw sectors (the sht value) in sysfs. You would have to add some modparam or try to add some patch to make it setable in sysfs. _______________________________________________ devel mailing list [email protected] http://www.open-fcoe.org/mailman/listinfo/devel
