Robert Pearson wrote:
Vlad,
I think we agree. But, when we tried the experiment of running without the
local memory allocator scst hung when we did large IO operations. Probably
something simple.
Why do you think it scst hung, not something else? Do you have evidences
for that? ;) According to Vu, you can't simply switch to SCST memory
allocator, because IB hardware has very limited number of available SG
entries in commands (few tens), so for large request, where there are
too many SG entries, they should be "iomapped" using the corresponding
IB facility.
We can look harder. Next step for us is to sync up with Vu
on a few other changes in the works.
Bob Pearson
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Vladislav
Bolkhovitin
Sent: Saturday, January 12, 2008 3:51 AM
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]; [email protected]
Subject: Re: [ofa-general] [PATCH][REPOST] drivers/infiniband/ulp/srpt:
Fixtarget data corruption
[EMAIL PROTECTED] wrote:
This is an updated version of [PATCH] drivers/infiniband/ulp/srpt: Fix
target data corruption
It was pointed out to me that the code to round up to a power of 2 was
not as clean as it should be, plus I extracted two unrelated patches and
submitted them separately.
=====================================================================
Change the local buffer allocator to use a spin-lock protected linked
list instead of an array of atomic_t used/free variables. The atomic_t
code was open to a multi-thread race between test and set. This has
been observed with the result that the same data buffer was used for
more than one SCSI operation, either writing the wrong data to the disk
or sending the wrong data to the initiator.
I, as a main SCST developer and implementor, would suggest to completely
remove internal memory management from the SRPT driver and use SCST
memory management instead. It will provide the following advantages:
1. Simplify SRPT driver and completely remove such kind of bugs.
2. Make SRPT target driver compatible with scst_user module, i.e. will
allow to use SRPT target driver with backstorage devices, implemented in
user space. Usual example of such devices is a VTL (Virtual Tape Library).
3. (Most likely, since I'm not too familiar with SRPT drivers internals,
but for me it looks like so) Allow SRPT driver to reliably work with
many outstanding commands with big data transfer sizes (>=1MB)
4. Might improve performance by caching and reusing already allocated
and "iomaped" to Infiniband hardware SG vectors. Vu knows the details,
we discussed them with him. It will require some minor SCST
modifications (extending its interface with target drivers), but I'm
willing to make them if somebody ask for it.
Vlad
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