netdev - RE: [PATCH net-next] net: dpaa: remove init which already done in per-cpu allocation

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Date:   Mon, 30 Oct 2017 07:13:41 +0000
From:   Madalin-cristian Bucur <madalin.bucur@....com>
To:     "Yuan, Linyu (NSB - CN/Shanghai)" <linyu.yuan@...ia-sbell.com>,
        yuan linyu <cugyly@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "David S . Miller" <davem@...emloft.net>
Subject: RE: [PATCH net-next] net: dpaa: remove init which already done in
 per-cpu allocation

+Eric

> -----Original Message-----
> From: Yuan, Linyu (NSB - CN/Shanghai) [mailto:linyu.yuan@...ia-sbell.com]
> 
> I just saw below accepted commit, it said "per cpu allocations are already
> zeroed, no need to clear them again."
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=bfd8e5a407133e58a92a38ccf3d0ba6db81f22d8
> 
> I will not touch memory sub-system, so I will not change this function
> description.
> 

Your particular change removes redundancy, it's fine. Having the memset documented
somewhere would prevent similar redundancy from being added in the future.

> > -----Original Message-----
> > From: Madalin-cristian Bucur [mailto:madalin.bucur@....com]
> > Sent: Monday, October 30, 2017 1:56 PM
> > To: Yuan, Linyu (NSB - CN/Shanghai); yuan linyu; netdev@...r.kernel.org;
> > gregkh@...uxfoundation.org
> > Cc: David S . Miller
> > Subject: RE: [PATCH net-next] net: dpaa: remove init which already done
> in
> > per-cpu allocation
> >
> > Also here:
> >
> >
> > http://elixir.free-electrons.com/linux/latest/source/mm/percpu.c#L717
> >
> > Should the fact that the memory is zeroed be included in the function
> > description?
> >
> > /**
> >  * pcpu_alloc - the percpu allocator
> >  * @size: size of area to allocate in bytes
> >  * @align: alignment of area (max PAGE_SIZE)
> >  * @reserved: allocate from the reserved chunk if available
> >  * @gfp: allocation flags
> >  *
> >  * Allocate percpu area of @size bytes aligned at @align.  If @gfp
> doesn't
> >  * contain %GFP_KERNEL, the allocation is atomic.
> >  *
> >  * RETURNS:
> >  * Percpu pointer to the allocated area on success, NULL on failure.
> >  */
> >
> > Now it seems to be an implementation detail rather than a guarantee.
> >
> > Looking at Documentation/driver-model/devres.txt, the memset is not
> > mentioned there either.
> >
> > > -----Original Message-----
> > > From: Yuan, Linyu (NSB - CN/Shanghai) [mailto:linyu.yuan@...ia-
> sbell.com]
> > > Sent: Monday, October 30, 2017 7:21 AM
> > > To: Madalin-cristian Bucur <madalin.bucur@....com>; yuan linyu
> > > <cugyly@....com>; netdev@...r.kernel.org
> > > Cc: David S . Miller <davem@...emloft.net>
> > > Subject: RE: [PATCH net-next] net: dpaa: remove init which already
> > > done in per-cpu allocation
> > >
> > > http://elixir.free-electrons.com/linux/latest/source/mm/percpu.c#L1018
> > >
> > > > -----Original Message-----
> > > > From: Madalin-cristian Bucur [mailto:madalin.bucur@....com]
> > > > Sent: Monday, October 30, 2017 1:15 PM
> > > > To: Yuan, Linyu (NSB - CN/Shanghai); yuan linyu;
> netdev@...r.kernel.org
> > > > Cc: David S . Miller
> > > > Subject: RE: [PATCH net-next] net: dpaa: remove init which already
> > > > done in per-cpu allocation
> > > >
> > > > Is the memset part documented?
> > > > Can you point to the specific comment & code that does it?
> > > >
> > > > Thanks
> > > >
> > > > > -----Original Message-----
> > > > > From: Yuan, Linyu (NSB - CN/Shanghai) [mailto:linyu.yuan@...ia-
> > > sbell.com]
> > > > > Sent: Monday, October 30, 2017 7:12 AM
> > > > > To: Madalin-cristian Bucur <madalin.bucur@....com>; yuan linyu
> > > > > <cugyly@....com>; netdev@...r.kernel.org
> > > > > Cc: David S . Miller <davem@...emloft.net>
> > > > > Subject: RE: [PATCH net-next] net: dpaa: remove init which already
> > > done in
> > > > > per-cpu allocation
> > > > >
> > > > > Hi,
> > > > >
> > > > > devm_alloc_percpu() will allocate per-cpu memory and memset
> allocated
> > > > > block content to 0.
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Madalin-cristian Bucur [mailto:madalin.bucur@....com]
> > > > > > Sent: Monday, October 30, 2017 1:08 PM
> > > > > > To: yuan linyu; netdev@...r.kernel.org
> > > > > > Cc: David S . Miller; Yuan, Linyu (NSB - CN/Shanghai)
> > > > > > Subject: RE: [PATCH net-next] net: dpaa: remove init which
> > > > > > already done in per-cpu allocation
> > > > > >
> > > > > > Hi Yuan,
> > > > > >
> > > > > > Can you please give more details about this change you are
> > > proposing?
> > > > > >
> > > > > > Regards,
> > > > > > Madalin
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: netdev-owner@...r.kernel.org
> > > > > > [mailto:netdev-owner@...r.kernel.org]
> > > > > > > On Behalf Of yuan linyu
> > > > > > > Sent: Sunday, October 29, 2017 3:49 AM
> > > > > > > To: netdev@...r.kernel.org
> > > > > > > Cc: David S . Miller <davem@...emloft.net>; yuan linyu
> > > > > > > <Linyu.Yuan@...atel-sbell.com.cn>
> > > > > > > Subject: [PATCH net-next] net: dpaa: remove init which already
> > > done in
> > > > > > > per-cpu allocation
> > > > > > >
> > > > > > > From: yuan linyu <Linyu.Yuan@...atel-sbell.com.cn>
> > > > > > >
> > > > > > > Signed-off-by: yuan linyu <Linyu.Yuan@...atel-sbell.com.cn>
> > > > > > > ---
> > > > > > >  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 4 ----
> > > > > > >  1 file changed, 4 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > > > > > > b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > > > > > > index a8d0be8..1ccc316 100644
> > > > > > > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > > > > > > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > > > > > > @@ -2814,10 +2814,6 @@ static int dpaa_eth_probe(struct
> > > > > > platform_device
> > > > > > > *pdev)
> > > > > > >  		err = -ENOMEM;
> > > > > > >  		goto free_dpaa_fqs;
> > > > > > >  	}
> > > > > > > -	for_each_possible_cpu(i) {
> > > > > > > -		percpu_priv = per_cpu_ptr(priv->percpu_priv, i);
> > > > > > > -		memset(percpu_priv, 0, sizeof(*percpu_priv));
> > > > > > > -	}
> > > > > > >
> > > > > > >  	priv->num_tc = 1;
> > > > > > >  	netif_set_real_num_tx_queues(net_dev, priv->num_tc *
> > > > > > > DPAA_TC_TXQ_NUM);
> > > > > > > --
> > > > > > > 2.7.4
> > > > > > >