IOs stuck in SG

[Mark Lobo]

I am seeing a problem where IOs get stuck in SG for a _long_ time. The 

initiator driver is our own, and we dont see any IOs in there that are 

pending. We are running 2.4.30.  

 

This is what I see in the proc file for SG. The act: acc to documentation 
means: 

act: mid level (adapter driver or device) has command. 

 

Has anyone seen this problem? If yes, is there a patch for this problem? 

 

>>> device=sg97 scsi4 chan=0 id=17 lun=0   em=0 sg_tablesize=64 excl=0 

   FD(1): timeout=6ms bufflen=4096 (res)sgat=0 low_dma=0 

   cmd_q=1 f_packid=1 k_orphan=0 closed=0 

 act: id=1856404224 blen=8 t_o/elap=15000/54615000ms sgat=0 op=0x25 

 >>> device=sg98 scsi4 chan=0 id=18 lun=0   em=0 sg_tablesize=64 excl=0 

   FD(1): timeout=6ms bufflen=4096 (res)sgat=0 low_dma=0 

   cmd_q=1 f_packid=1 k_orphan=0 closed=0 

 act: id=1883362756 blen=255 t_o/elap=15000/54474000ms sgat=0 op=0x1c 

 

 

-- Mark 












 

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Disabling block layer

[Mark Lobo]

Hello!

I had a question about disabling the block layer for SCSI devices. We
have an embedded device, and it runs 2.4.30. We need to be able to
support a lot of SCSI devices (in the thousands) for our device, and we
talk to the devices via SG. We are facing a memory allocation problem
after discovering a few thousand devices. For every device,  there
seems to be a lot of memory allocated in the block layer. This memory
includes cache memory (which IIRC is reclaimable by the kernel memory
subsystem when it needs it) and also pages that are used for the
alloc_pages pool.



My questions were relating to disabling the block layer for the
devices. We always talk direct passthrough to the storage(except the
local hard disk),  and do not need the block layer at all. 

1. Is there a way to disable the block layer for specific devices?

2. If yes, how can that be done, and  are there any gotchas associated with 
that?



Thanks!

M


 

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