linux-kernel - Re: [PATCH 5/7] Documentation: DT: net: cpsw: allow to specify descriptors pool size

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Date:   Wed, 7 Dec 2016 13:41:49 -0600
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
CC:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        Mugunthan V N <mugunthanvnm@...com>,
        Sekhar Nori <nsekhar@...com>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 5/7] Documentation: DT: net: cpsw: allow to specify
 descriptors pool size



On 12/02/2016 11:21 AM, Grygorii Strashko wrote:
> 
> 
> On 12/02/2016 05:28 AM, Ivan Khoronzhuk wrote:
>> On Thu, Dec 01, 2016 at 05:34:30PM -0600, Grygorii Strashko wrote:
>>> Add optional property "descs_pool_size" to specify buffer descriptor's
>>> pool size. The "descs_pool_size" should define total number of CPDMA
>>> CPPI descriptors to be used for both ingress/egress packets
>>> processing. If not specified - the default value 256 will be used
>>> which will allow to place descriptor's pool into the internal CPPI
>>> RAM on most of TI SoC.
>>>
>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>> ---
>>>  Documentation/devicetree/bindings/net/cpsw.txt | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/net/cpsw.txt b/Documentation/devicetree/bindings/net/cpsw.txt
>>> index 5ad439f..b99d196 100644
>>> --- a/Documentation/devicetree/bindings/net/cpsw.txt
>>> +++ b/Documentation/devicetree/bindings/net/cpsw.txt
>>> @@ -35,6 +35,11 @@ Optional properties:
>>>  			  For example in dra72x-evm, pcf gpio has to be
>>>  			  driven low so that cpsw slave 0 and phy data
>>>  			  lines are connected via mux.
>>> +- descs_pool_size	: total number of CPDMA CPPI descriptors to be used for
>>> +			  both ingress/egress packets processing. if not
>>> +			  specified the default value 256 will be used which
>>> +			  will allow to place descriptors pool into the
>>> +			  internal CPPI RAM.
>> Does it describe h/w? Why now module parameter? or even smth like ethtool num
>> ring entries?
>>
> 
> It can be module parameter too. for the use cases i'm aware of -
> this is one-time boot setting only.  
> 
> ----- OR
> So, do you propose to use 
>        ethtool -g ethX
> 
>        ethtool -G ethX [rx N] [tx N]
> ?
> 
> Now cpdma has one pool for all RX/TX channels, so changing this settings
> by ethtool will require: pause interfaces, reallocate cpdma pool, 
> re-arrange buffers between channels, resume interface. Correct?
> 
> How do you think - we can move forward with one pool or better to have two (Rx and Tx)?
> 
> Wouldn't it be reasonable to still have DT (or module) parameter to avoid 
> cpdma reconfiguration on system startup (pause/resume interfaces) (faster boot)?
> 
> How about cpdma re-allocation policy (with expectation that is shouldn't happen too often)?
> - increasing of Rx, Tx will grow total number of physically allocated buffers (total_desc_num)
> - decreasing of Rx, Tx will just change number of available buffers (no memory re-allocation)
> 
> ----- OR ----
> Can we move forward with current patch (total number of CPDMA CPPI descriptors defined in DT) 
> and add ethtool -G ethX [rx N] [tx N] which will allow to re-split descs between RX and TX?
> 
> 

if no comments here, I'll rework patches to use module parameter for descs_pool_size and
will add possibility to re-split RX/TX buffers using  ethtool -G ethX [rx N] [tx N]

-- 
regards,
-grygorii