linux-kernel - Re: [PATCH v2 1/2] Introduce maximum WQE size to check limits

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Date:   Tue, 19 Nov 2019 19:13:34 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Rao Shoaib <rao.shoaib@...cle.com>
Cc:     monis@...lanox.com, dledford@...hat.com, sean.hefty@...el.com,
        hal.rosenstock@...il.com, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] Introduce maximum WQE size to check limits

On Tue, Nov 19, 2019 at 02:38:23PM -0800, Rao Shoaib wrote:
> 
> On 11/19/19 12:31 PM, Jason Gunthorpe wrote:
> > On Mon, Nov 18, 2019 at 11:54:38AM -0800, rao Shoaib wrote:
> > > From: Rao Shoaib <rao.shoaib@...cle.com>
> > > 
> > > Introduce maximum WQE size to impose limits on max SGE's and inline data
> > > 
> > > Signed-off-by: Rao Shoaib <rao.shoaib@...cle.com>
> > >   drivers/infiniband/sw/rxe/rxe_param.h | 3 ++-
> > >   drivers/infiniband/sw/rxe/rxe_qp.c    | 7 +++++--
> > >   2 files changed, 7 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/infiniband/sw/rxe/rxe_param.h b/drivers/infiniband/sw/rxe/rxe_param.h
> > > index 1b596fb..31fb5c7 100644
> > > +++ b/drivers/infiniband/sw/rxe/rxe_param.h
> > > @@ -68,7 +68,6 @@ enum rxe_device_param {
> > >   	RXE_HW_VER			= 0,
> > >   	RXE_MAX_QP			= 0x10000,
> > >   	RXE_MAX_QP_WR			= 0x4000,
> > > -	RXE_MAX_INLINE_DATA		= 400,
> > >   	RXE_DEVICE_CAP_FLAGS		= IB_DEVICE_BAD_PKEY_CNTR
> > >   					| IB_DEVICE_BAD_QKEY_CNTR
> > >   					| IB_DEVICE_AUTO_PATH_MIG
> > > @@ -79,7 +78,9 @@ enum rxe_device_param {
> > >   					| IB_DEVICE_RC_RNR_NAK_GEN
> > >   					| IB_DEVICE_SRQ_RESIZE
> > >   					| IB_DEVICE_MEM_MGT_EXTENSIONS,
> > > +	RXE_MAX_WQE_SIZE		= 0x2d0, /* For RXE_MAX_SGE */
> > This shouldn't just be a random constant, I think you are trying to
> > say:
> > 
> >    RXE_MAX_WQE_SIZE = sizeof(struct rxe_send_wqe) + sizeof(struct ib_sge)*RXE_MAX_SGE

> I thought you wanted this value to be independent of RXE_MAX_SGE, else why
> are defining it.

Then define 

   RXE_MAX_SGE = (RXE_MAX_WQE_SIZE - sizeof(rxe_send_wqe))/sizeof(rxe_sge)

And drive everything off RXE_MAX_WQE_SIZE, which sounds good

> > Just say that
> > 
> > >   	RXE_MAX_SGE			= 32,
> > > +	RXE_MAX_INLINE_DATA		= RXE_MAX_WQE_SIZE,
> > This is mixed up now, it should be
> > 
> >    RXE_MAX_INLINE_DATA = RXE_MAX_WQE_SIZE - sizeof(rxe_send_wqe)
> 
> I agree to what you are suggesting, it will make the current patch better.
> However, In my previous patch I had
> 
> RXE_MAX_INLINE_DATA		= RXE_MAX_SGE * sizeof(struct ib_sge)
> 
> IMHO that conveys the intent much better. I do not see the reason for
> defining RXE_MAX_WQE_SIZE, ib_device_attr does not even have an entry for it
> and hence the value is not used anywhere by rxe or by any other relevant
> driver.

Because WQE_SIZE is what you are actually concerned with here, using
MAX_SGE as a proxy for the max WQE is confusing

Jason