linux-kernel - Re: [PATCH v3 18/18] NTB: Increase transport MTU to 64k from 16k

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Date:	Tue, 9 Jun 2015 16:45:36 +0000
From:	"Jiang, Dave" <dave.jiang@...el.com>
To:	"bhelgaas@...gle.com" <bhelgaas@...gle.com>
CC:	"Allen.Hubbe@....com" <Allen.Hubbe@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"jdmason@...zu.us" <jdmason@...zu.us>,
	"linux-ntb@...glegroups.com" <linux-ntb@...glegroups.com>
Subject: Re: [PATCH v3 18/18] NTB: Increase transport MTU to 64k from 16k

On Tue, 2015-06-09 at 11:04 -0500, 'Bjorn Helgaas' via linux-ntb wrote:
> On Tue, Jun 9, 2015 at 4:44 AM, Allen Hubbe <Allen.Hubbe@....com> 
> wrote:
> > From: Dave Jiang <dave.jiang@...el.com>
> > 
> > Benchmarking showed significant performance increase going from MTU 
> > size
> > of 64k from 16k.  Changing the default.
> 
> This changelog doesn't parse.  I think you mean "going from MTU size
> 16k to 64k."

Yes. Sorry about the confusion.

> 
> The original value was 0x401e (16k + 0x1e), and the new value is
> exactly 64k.  Please include a note about what that extra 0x1e was 
> for
> and why it isn't needed in the new value.

Jon, can you comment on why there's the additional 30 bytes on top of
16k in the previous value? 

> 
> > Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> > ---
> >  drivers/ntb/ntb_transport.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/ntb/ntb_transport.c 
> > b/drivers/ntb/ntb_transport.c
> > index ea237aeca28c..c87bc0cbd607 100644
> > --- a/drivers/ntb/ntb_transport.c
> > +++ b/drivers/ntb/ntb_transport.c
> > @@ -76,7 +76,7 @@ static unsigned long max_mw_size;
> >  module_param(max_mw_size, ulong, 0644);
> >  MODULE_PARM_DESC(max_mw_size, "Limit size of large memory 
> > windows");
> > 
> > -static unsigned int transport_mtu = 0x401E;
> > +static unsigned int transport_mtu = 0x10000;
> >  module_param(transport_mtu, uint, 0644);
> >  MODULE_PARM_DESC(transport_mtu, "Maximum size of NTB transport 
> > packets");
> > 
> > --
> > 2.4.0.rc0.43.gcf8a8c6
> > 
> > --
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