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From: Borislav Petkov <bp@alien8.de>
To: Ashish Kalra <Ashish.Kalra@amd.com>
Cc: Thomas.Lendacky@amd.com, Jon.Grimm@amd.com,
	brijesh.singh@amd.com, dave.hansen@linux-intel.com,
	konrad.wilk@oracle.com, peterz@infradead.org, x86@kernel.org,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	mingo@redhat.com, luto@kernel.org, hpa@zytor.com,
	rientjes@google.com, tglx@linutronix.de, hch@lst.de
Subject: Re: [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.
Date: Mon, 7 Dec 2020 13:10:07 +0100	[thread overview]
Message-ID: <20201207121007.GD20489@zn.tnic> (raw)
In-Reply-To: <20201203032559.3388-1-Ashish.Kalra@amd.com>

On Thu, Dec 03, 2020 at 03:25:59AM +0000, Ashish Kalra wrote:
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 1bcfbcd2bfd7..46549bd3d840 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -485,7 +485,38 @@ static void print_mem_encrypt_feature_info(void)
>  	pr_cont("\n");
>  }

Any text about why 6% was chosen? A rule of thumb or so? Measurements?

> +#define SEV_ADJUST_SWIOTLB_SIZE_PERCENT	6
> +
>  /* Architecture __weak replacement functions */
> +unsigned long __init arch_swiotlb_adjust(unsigned long iotlb_default_size)
> +{
> +	unsigned long size = iotlb_default_size;
> +
> +	/*
> +	 * For SEV, all DMA has to occur via shared/unencrypted pages.
> +	 * SEV uses SWOTLB to make this happen without changing device
> +	 * drivers. However, depending on the workload being run, the
> +	 * default 64MB of SWIOTLB may not be enough and`SWIOTLB may
> +	 * run out of buffers for DMA, resulting in I/O errors and/or
> +	 * performance degradation especially with high I/O workloads.
> +	 * Adjust the default size of SWIOTLB for SEV guests using
> +	 * a percentage of guest memory for SWIOTLB buffers.
> +	 * Also as the SWIOTLB bounce buffer memory is allocated
> +	 * from low memory, ensure that the adjusted size is within
> +	 * the limits of low available memory.
> +	 *
> +	 */
> +	if (sev_active()) {
> +		phys_addr_t total_mem = memblock_phys_mem_size();

Please integrate scripts/checkpatch.pl into your patch creation
workflow. Some of the warnings/errors *actually* make sense:

WARNING: Missing a blank line after declarations
#95: FILE: arch/x86/mm/mem_encrypt.c:511:
+               phys_addr_t total_mem = memblock_phys_mem_size();
+               size = total_mem * SEV_ADJUST_SWIOTLB_SIZE_PERCENT / 100;

But no need to resend now - just a hint for the future.

Konrad, ack?

On a 2G guest here, it says:

[    0.018373] SWIOTLB bounce buffer size adjusted to 122MB for SEV

so it makes sense to me.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette
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iommu@lists.linux-foundation.org
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WARNING: multiple messages have this Message-ID (diff)
From: Borislav Petkov <bp@alien8.de>
To: Ashish Kalra <Ashish.Kalra@amd.com>
Cc: konrad.wilk@oracle.com, hch@lst.de, tglx@linutronix.de,
	mingo@redhat.com, hpa@zytor.com, x86@kernel.org, luto@kernel.org,
	peterz@infradead.org, dave.hansen@linux-intel.com,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	brijesh.singh@amd.com, Thomas.Lendacky@amd.com,
	Jon.Grimm@amd.com, rientjes@google.com
Subject: Re: [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.
Date: Mon, 7 Dec 2020 13:10:07 +0100	[thread overview]
Message-ID: <20201207121007.GD20489@zn.tnic> (raw)
In-Reply-To: <20201203032559.3388-1-Ashish.Kalra@amd.com>

On Thu, Dec 03, 2020 at 03:25:59AM +0000, Ashish Kalra wrote:
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 1bcfbcd2bfd7..46549bd3d840 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -485,7 +485,38 @@ static void print_mem_encrypt_feature_info(void)
>  	pr_cont("\n");
>  }

Any text about why 6% was chosen? A rule of thumb or so? Measurements?

> +#define SEV_ADJUST_SWIOTLB_SIZE_PERCENT	6
> +
>  /* Architecture __weak replacement functions */
> +unsigned long __init arch_swiotlb_adjust(unsigned long iotlb_default_size)
> +{
> +	unsigned long size = iotlb_default_size;
> +
> +	/*
> +	 * For SEV, all DMA has to occur via shared/unencrypted pages.
> +	 * SEV uses SWOTLB to make this happen without changing device
> +	 * drivers. However, depending on the workload being run, the
> +	 * default 64MB of SWIOTLB may not be enough and`SWIOTLB may
> +	 * run out of buffers for DMA, resulting in I/O errors and/or
> +	 * performance degradation especially with high I/O workloads.
> +	 * Adjust the default size of SWIOTLB for SEV guests using
> +	 * a percentage of guest memory for SWIOTLB buffers.
> +	 * Also as the SWIOTLB bounce buffer memory is allocated
> +	 * from low memory, ensure that the adjusted size is within
> +	 * the limits of low available memory.
> +	 *
> +	 */
> +	if (sev_active()) {
> +		phys_addr_t total_mem = memblock_phys_mem_size();

Please integrate scripts/checkpatch.pl into your patch creation
workflow. Some of the warnings/errors *actually* make sense:

WARNING: Missing a blank line after declarations
#95: FILE: arch/x86/mm/mem_encrypt.c:511:
+               phys_addr_t total_mem = memblock_phys_mem_size();
+               size = total_mem * SEV_ADJUST_SWIOTLB_SIZE_PERCENT / 100;

But no need to resend now - just a hint for the future.

Konrad, ack?

On a 2G guest here, it says:

[    0.018373] SWIOTLB bounce buffer size adjusted to 122MB for SEV

so it makes sense to me.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2020-12-07 12:12 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-03  3:25 [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests Ashish Kalra
2020-12-03  3:25 ` Ashish Kalra
2020-12-07 12:10 ` Borislav Petkov [this message]
2020-12-07 12:10   ` Borislav Petkov
2020-12-07 22:06   ` Ashish Kalra
2020-12-07 22:06     ` Ashish Kalra
2020-12-07 22:14     ` Borislav Petkov
2020-12-07 22:14       ` Borislav Petkov
2020-12-07 22:20       ` Kalra, Ashish
2020-12-07 22:20         ` Kalra, Ashish
2020-12-07 22:33         ` Borislav Petkov
2020-12-07 22:33           ` Borislav Petkov

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