Re: [PATCH v1 2/2] dma-mapping-common: add DMA attribute - DMA_ATTR_IOMMU_BYPASS

[Shamir Rabinovitch]

On Thu, Nov 05, 2015 at 04:11:21PM -0500, David Miller wrote:
> 
> And for the record Sowmini fixed a lot of the lock contention:
> 
> commit ff7d37a502022149655c18035b99a53391be0383
> Author: Sowmini Varadhan 
> Date:   Thu Apr 9 15:33:30 2015 -0400
> 
> Break up monolithic iommu table/lock into finer graularity pools and lock
> 

The poor rds-stress results w/o IOMMU bypass I sent in early post were taken 
from
kernel that has the above patch and that has all the needed changes in 
arch/sparc
to use this new feature.

It seems that it worked well for 10G ETH IOMMU lock contention but it still not 
solving
the rds-stress issue.

The difference can be from:

1. Lock contention still left with this enhancement <-- zero in bypass
2. Overhead to setup the IOMMU mapping <-- almost zero in bypass (require 1 HV 
call)
3. Overhead to use the IOMMU mapping <-- not sure how to measure this
4. Overhead to tear the IOMMU mapping <-- zero in bypass 


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Re: [PATCH 1/3] context_tracking: remove duplicate enabled check

[Paolo Bonzini]

On 28/10/2015 06:19, Andy Lutomirski wrote:
> On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini  wrote:
>> All calls to context_tracking_enter and context_tracking_exit
>> are already checking context_tracking_is_enabled, except the
>> context_tracking_user_enter and context_tracking_user_exit
>> functions left in for the benefit of assembly calls.
>>
>> Pull the check up to those functions, by making them simple
>> wrappers around the user_enter and user_exit inline functions.
> 
> This makes my brain hurt.  Assuming that this survives a boot with
> CONFIG_CONTEXT_TRACKING_FORCE=y and CONFIG_PROVE_LOCKING=y (with the
> implied CONFIG_PROVE_RCU), then:
> 
> Acked-by: Andy Lutomirski 

Tested now.

Paolo
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