Re: [Qemu-devel] [PATCH] Improve DMA transfers by increasing the buffer size.

[Aurelien Jarno]

On Wed, Mar 26, 2008 at 04:35:00PM +0000, Ian Jackson wrote:
Content-Description: message body text
> In this patch we increase the DMA buffers in the ide emulation from 8k
> to 132k, and make it configurable separately from the MAX_MULT_SECTORS
> for maximum multi-mode transfers.  This can improve the performance in
> some conditions.
> 
> The patch is cross-ported from xen-unstable hg changeset
>  f4a92f0db20fda98a633c149e3396c005a759a77
> 
> Signed-off-by: Ian Jackson <address@hidden>
> Signed-off-by: Samuel Thibault <address@hidden>
> 

Content-Description: increase ide DMA buffers
> From 4eaa19458262cce92f0b891c51433ccee0a19b79 Mon Sep 17 00:00:00 2001
> From: Ian Jackson <address@hidden>
> Date: Wed, 26 Mar 2008 16:09:35 +0000
> Subject: [PATCH] Improve DMA transfers by increasing the size of DMA buffers.
> 
> This involves a new constant IDE_DMA_BUF_SIZE which is separate from
> MAX_MULT_SECTORS.
> 
> Cross-ported from xen-unstable
>  17267:f4a92f0db20fda98a633c149e3396c005a759a77
> 
> Signed-off-by: Ian Jackson <address@hidden>
> Signed-off-by: Samuel Thibault <address@hidden>
> ---
>  hw/ide.c |   20 +++++++++++++-------
>  1 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/ide.c b/hw/ide.c
> index 56a1cda..b73dba2 100644
> --- a/hw/ide.c
> +++ b/hw/ide.c
> @@ -202,6 +202,12 @@
>  /* set to 1 set disable mult support */
>  #define MAX_MULT_SECTORS 16
>  
> +#define IDE_DMA_BUF_SIZE 131072

Wouldn't it be better to define this value in number of sectors? This
would avoid a few divisions in the code, and anyway the code handling
DMA transfers is working with a number of sectors, not a number of 
bytes.

> +#if (IDE_DMA_BUF_SIZE < MAX_MULT_SECTORS * 512)
> +#error "IDE_DMA_BUF_SIZE must be bigger or equal to MAX_MULT_SECTORS * 512"
> +#endif
> +
>  /* ATAPI defines */
>  
>  #define ATAPI_PACKET_SIZE 12
> @@ -920,8 +926,8 @@ static void ide_read_dma_cb(void *opaque, int ret)
>  
>      /* launch next transfer */
>      n = s->nsector;
> -    if (n > MAX_MULT_SECTORS)
> -        n = MAX_MULT_SECTORS;
> +    if (n > IDE_DMA_BUF_SIZE / 512)
> +        n = IDE_DMA_BUF_SIZE / 512;
>      s->io_buffer_index = 0;
>      s->io_buffer_size = n * 512;
>  #ifdef DEBUG_AIO
> @@ -1028,8 +1034,8 @@ static void ide_write_dma_cb(void *opaque, int ret)
>  
>      /* launch next transfer */
>      n = s->nsector;
> -    if (n > MAX_MULT_SECTORS)
> -        n = MAX_MULT_SECTORS;
> +    if (n > IDE_DMA_BUF_SIZE / 512)
> +        n = IDE_DMA_BUF_SIZE / 512;
>      s->io_buffer_index = 0;
>      s->io_buffer_size = n * 512;
>  
> @@ -1323,8 +1329,8 @@ static void ide_atapi_cmd_read_dma_cb(void *opaque, int 
> ret)
>          data_offset = 16;
>      } else {
>          n = s->packet_transfer_size >> 11;
> -        if (n > (MAX_MULT_SECTORS / 4))
> -            n = (MAX_MULT_SECTORS / 4);
> +        if (n > (IDE_DMA_BUF_SIZE / 2048))
> +            n = (IDE_DMA_BUF_SIZE / 2048);
>          s->io_buffer_size = n * 2048;
>          data_offset = 0;
>      }
> @@ -2557,7 +2563,7 @@ static void ide_init2(IDEState *ide_state,
>  
>      for(i = 0; i < 2; i++) {
>          s = ide_state + i;
> -        s->io_buffer = qemu_memalign(512, MAX_MULT_SECTORS*512 + 4);
> +        s->io_buffer = qemu_memalign(512, IDE_DMA_BUF_SIZE + 4);
>          if (i == 0)
>              s->bs = hd0;
>          else
> -- 
> 1.4.4.4
> 


-- 
  .''`.  Aurelien Jarno             | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   address@hidden         | address@hidden
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