linux-kernel - Re: [PATCH v4.4-rc8 v2] dmaengine: ioatdma: Squelch framesize warnings

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Date:	Fri, 8 Jan 2016 08:39:30 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Tim Gardner <tim.gardner@...onical.com>
Cc:	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Nicholas Mc Guire <der.herr@...r.at>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Subject: Re: [PATCH v4.4-rc8 v2] dmaengine: ioatdma: Squelch framesize warnings

On Fri, Jan 8, 2016 at 5:35 AM,  <tim.gardner@...onical.com> wrote:
> From: Tim Gardner <tim.gardner@...onical.com>
>
>   CC [M]  drivers/dma/ioat/prep.o
> drivers/dma/ioat/prep.c: In function 'ioat_prep_pqxor':
> drivers/dma/ioat/prep.c:682:1: warning: the frame size of 1048 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>  }
>  ^
> drivers/dma/ioat/prep.c: In function 'ioat_prep_pqxor_val':
> drivers/dma/ioat/prep.c:714:1: warning: the frame size of 1048 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>  }
>
> gcc version 5.3.1 20151219 (Ubuntu 5.3.1-4ubuntu1)
>
> Cc: Vinod Koul <vinod.koul@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Prarit Bhargava <prarit@...hat.com>
> Cc: Nicholas Mc Guire <der.herr@...r.at>
> Cc: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> ---
>
> v2 - use per CPU static buffers instead of dynamically allocating memory.
>
>  drivers/dma/ioat/prep.c | 33 +++++++++++++++++++++++++++++----
>  1 file changed, 29 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/ioat/prep.c b/drivers/dma/ioat/prep.c
> index 6bb4a13..2c0768b 100644
> --- a/drivers/dma/ioat/prep.c
> +++ b/drivers/dma/ioat/prep.c
> @@ -21,6 +21,8 @@
>  #include <linux/dmaengine.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/prefetch.h>
> +#include <linux/percpu.h>
> +#include <linux/preempt.h>
>  #include "../dmaengine.h"
>  #include "registers.h"
>  #include "hw.h"
> @@ -655,13 +657,25 @@ ioat_prep_pq_val(struct dma_chan *chan, dma_addr_t *pq, dma_addr_t *src,
>                                      flags);
>  }
>
> +/*
> + * The scf scratch buffer is too large for an automatic variable, and
> + * we don't want to take the performance hit for dynamic allocation.
> + * Therefore, define per CPU buffers and disable preemption while in use.
> + */
> +static DEFINE_PER_CPU(unsigned char [MAX_SCF], ioat_scf);
> +static inline unsigned char *ioat_assign_scratch_buffer(void)
> +{
> +       return get_cpu_var(ioat_scf);

This get needs to be paired with a put_cpu_var().

> +}
> +
>  struct dma_async_tx_descriptor *
>  ioat_prep_pqxor(struct dma_chan *chan, dma_addr_t dst, dma_addr_t *src,
>                  unsigned int src_cnt, size_t len, unsigned long flags)
>  {
> -       unsigned char scf[MAX_SCF];
> +       unsigned char *scf;
>         dma_addr_t pq[2];
>         struct ioatdma_chan *ioat_chan = to_ioat_chan(chan);
> +       struct dma_async_tx_descriptor *desc;
>
>         if (test_bit(IOAT_CHAN_DOWN, &ioat_chan->state))
>                 return NULL;
> @@ -669,16 +683,21 @@ ioat_prep_pqxor(struct dma_chan *chan, dma_addr_t dst, dma_addr_t *src,
>         if (src_cnt > MAX_SCF)
>                 return NULL;
>
> +       preempt_disable();

preempt_disable() is embedded in get_cpu_var(), no need to open code it.

> +       scf = ioat_assign_scratch_buffer();
> +
>         memset(scf, 0, src_cnt);
>         pq[0] = dst;
>         flags |= DMA_PREP_PQ_DISABLE_Q;
>         pq[1] = dst; /* specify valid address for disabled result */
>
> -       return src_cnt_flags(src_cnt, flags) > 8 ?
> +       desc = src_cnt_flags(src_cnt, flags) > 8 ?
>                 __ioat_prep_pq16_lock(chan, NULL, pq, src, src_cnt, scf, len,
>                                        flags) :
>                 __ioat_prep_pq_lock(chan, NULL, pq, src, src_cnt, scf, len,
>                                      flags);
> +       preempt_enable();

put_cpu_var()...