Re: [PATCH 0/3] megaraid_sas: Convert to host_lock less w/ interrupts disabled internally

[Hannes Reinecke <hare@suse.de>]

On 11/28/2010 08:28 AM, Nicholas A. Bellinger wrote:
> On Sat, 2010-11-27 at 23:17 -0800, Nicholas A. Bellinger wrote:
>> From: Nicholas Bellinger <nab@linux-iscsi.org>
>>
>> Greetings Hannes, Bo and Co,
>>
>> This series converts megaraid_sas to run in modern host_lock-less mode
>> for >= .37-rc3+ with interrupts disabled internally around megasas_instance->hba_lock.
>> This series is currently living in lio-core-2.6.git/lock_less-LLDs-for-38-v2,
>> and is intended for .38 mainline code.
>>
>> The first patch adds a handful of missing barriers around instance->fw_outstanding
>> usage w/ atomic_add() and atomic_dec().
>>
>> The second converts instance->issuepend_done to an atomic_t, along with
>> the necessary assignments in order to run w/ Scsi_Host->host_lock, and
>> without instance->hba_lock.
>>
>> The third patch does the actual conversion, and adds a __megasas_get_cmd()
>> usased by megasas_queue_command() w/ instance->hba_lock, along with
>> being held for megasas_build_ldio() and megasas_build_dcdb() in order
>> to locate the proper frame for struct megasas_cmd.  This is really the
>> one major change in order to get host_lock-less to function with interrupts
>> disabled around hba_lock.
>>
>> So far this has been tested with Hannes's QEMU 8708EM2 HBA emulation with
>> TCM_Loop backends using SG_IO from KVM host in a paired Host/Guest .37-rc3
>> environment.  This has not been tested on real silicon yet, but I believe
>> this series should be working there as well.
>>
> 
> And quick screenshot running in KVM Host TCM_Loop host_lock-less mode
> into KVM Guest megaraid_sas host_lock-less mode w/ small block LTP
> disktest.
> 
> http://www.linux-iscsi.org/index.php/File:TCM_loop-megasas-37-rc3.png
> 
> Just a FYI, with scsi-generic <-> TCM_Loop everything appears to be
> stable for both small and large block size tests.
> 
Oh, good. I did some initial tests with megaraid_sas & host_lock
disabled, but ran into the problems you mentioned.
And have been too lazy to pursue this problem further.
Thanks for your work; I'll give it a spin and see if the throughput
speed has increased.

Thanks for the patches.

Btw, I've found one issue wrt Windows7 booting; now we're not
crashing anymore. But we're not exactly progressing, either;
apparently Win7 fails to notify that we've finished the commands.
Continue debugging.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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