From: Andi Kleen <andi@firstfloor.org>
To: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: konrad.wilk@oracle.com, tglx@linutronix.de, mingo@redhat.com,
hpa@zytor.com, rob@landley.net, akpm@linux-foundation.org,
joerg.roedel@amd.com, bhelgaas@google.com, shuahkhan@gmail.com,
linux-kernel@vger.kernel.org, devel@linuxdriverproject.org,
x86@kernel.org, torvalds@linux-foundation.org
Subject: Re: [RFC PATCH 0/7] Improve swiotlb performance by using physical addresses
Date: Fri, 05 Oct 2012 09:55:39 -0700 [thread overview]
Message-ID: <m28vbkx3hw.fsf@firstfloor.org> (raw)
In-Reply-To: <20121004002113.5016.66913.stgit@gitlad.jf.intel.com> (Alexander Duyck's message of "Wed, 03 Oct 2012 17:38:41 -0700")
Alexander Duyck <alexander.h.duyck@intel.com> writes:
> While working on 10Gb/s routing performance I found a significant amount of
> time was being spent in the swiotlb DMA handler. Further digging found that a
> significant amount of this was due to the fact that virtual to physical
> address translation and calling the function that did it. It accounted for
> nearly 60% of the total overhead.
Can you find out why that is? Traditionally virt_to_phys was just a
subtraction. Then later on it was a if and a subtraction.
It cannot really be that expensive. Do you have some debugging enabled?
Really virt_to_phys should be fixed. Such fundamental operations
shouldn't slow. I don't think hacking up all the users to work
around this is the r ight way.
Looking at the code a bit someone (crazy) made it out of line.
But that cannot explain that much overhead.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
next prev parent reply other threads:[~2012-10-05 16:55 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-04 0:38 [RFC PATCH 0/7] Improve swiotlb performance by using physical addresses Alexander Duyck
2012-10-04 0:38 ` [RFC PATCH 1/7] swiotlb: Instead of tracking the end of the swiotlb region just calculate it Alexander Duyck
2012-10-04 13:01 ` Konrad Rzeszutek Wilk
2012-10-04 15:54 ` Alexander Duyck
2012-10-04 16:31 ` Konrad Rzeszutek Wilk
2012-10-04 0:38 ` [RFC PATCH 2/7] swiotlb: Make io_tlb_start a physical address instead of a virtual address Alexander Duyck
2012-10-04 13:18 ` Konrad Rzeszutek Wilk
2012-10-04 17:11 ` Alexander Duyck
2012-10-04 17:19 ` Konrad Rzeszutek Wilk
2012-10-04 20:22 ` Alexander Duyck
2012-10-09 16:43 ` Konrad Rzeszutek Wilk
2012-10-09 19:11 ` Alexander Duyck
2012-10-04 0:38 ` [RFC PATCH 3/7] swiotlb: Make io_tlb_overflow_buffer a physical address Alexander Duyck
2012-10-04 0:39 ` [RFC PATCH 4/7] swiotlb: Return physical addresses when calling swiotlb_tbl_map_single Alexander Duyck
2012-10-04 0:39 ` [RFC PATCH 5/7] swiotlb: Use physical addresses for swiotlb_tbl_unmap_single Alexander Duyck
2012-10-04 0:39 ` [RFC PATCH 6/7] swiotlb: Use physical addresses instead of virtual in swiotlb_tbl_sync_single Alexander Duyck
2012-10-04 0:39 ` [RFC PATCH 7/7] swiotlb: Do not export swiotlb_bounce since there are no external consumers Alexander Duyck
2012-10-04 12:55 ` [RFC PATCH 0/7] Improve swiotlb performance by using physical addresses Konrad Rzeszutek Wilk
2012-10-04 15:50 ` Alexander Duyck
2012-10-04 13:33 ` Konrad Rzeszutek Wilk
2012-10-04 17:57 ` Alexander Duyck
2012-10-05 16:55 ` Andi Kleen [this message]
2012-10-05 19:35 ` Alexander Duyck
2012-10-05 20:02 ` Andi Kleen
2012-10-05 23:23 ` Alexander Duyck
2012-10-06 17:57 ` Andi Kleen
2012-10-06 18:56 ` H. Peter Anvin
2012-10-08 15:43 ` Alexander Duyck
2012-10-09 19:05 ` Alexander Duyck
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