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Re: [Qemu-devel] [PATCH qemu] spapr_pci: Warn when RAM page size is not


From: David Gibson
Subject: Re: [Qemu-devel] [PATCH qemu] spapr_pci: Warn when RAM page size is not enabled in IOMMU page mask
Date: Wed, 29 Mar 2017 16:10:32 +1100
User-agent: Mutt/1.8.0 (2017-02-23)

On Tue, Mar 28, 2017 at 07:13:49PM +1100, Alexey Kardashevskiy wrote:
> If a page size used by QEMU is not enabled in the PHB IOMMU page mask,
> in-kernel acceleration of TCE handling won't be enabled and performance
> might be slower than expected.
> 
> This prints a warning if system page size is not enabled. This should
> print a warning if huge pages are enabled but sphb.pgsz still uses
> the default value of 4K|64K.
> 
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> ---
> 
> This follow-up for "exec, spapr_pci: Advertise huge IOMMU pages".
> Instead of silently changing PHB properties+behaviour for better
> performance if huge pages are detected, this simply warns the user
> if IOMMU page mask needs to be adjusted. Since the user chooses
> huge pages in the first place, the user can also supply additional
> page masks as well.

Applied to ppc-for-2.10.

> 
> 
> ---
>  hw/ppc/spapr_pci.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index 98c52e411f..097ebdd51d 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -1771,6 +1771,12 @@ static void spapr_phb_realize(DeviceState *dev, Error 
> **errp)
>      }
>  
>      /* DMA setup */
> +    if ((sphb->page_size_mask & qemu_getrampagesize()) == 0) {
> +        error_report("System page size 0x%lx is not enabled in 
> page_size_mask "
> +                     "(0x%"PRIx64"). Performance may be slow",
> +                     qemu_getrampagesize(), sphb->page_size_mask);
> +    }
> +
>      for (i = 0; i < windows_supported; ++i) {
>          tcet = spapr_tce_new_table(DEVICE(sphb), sphb->dma_liobn[i]);
>          if (!tcet) {

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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