On 17-Jul-18 10:22 AM, Xu, Qian Q wrote:
-----Original Message-----
From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Burakov, Anatoly
Sent: Monday, July 16, 2018 10:01 PM
To: Stojaczyk, DariuszX <dariuszx.stojac...@intel.com>; dev@dpdk.org
Cc: sta...@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] memory: fix alignment in eal_get_virtual_area()
On 16-Jul-18 2:29 PM, Stojaczyk, DariuszX wrote:
-----Original Message-----
From: Burakov, Anatoly
Sent: Monday, July 16, 2018 2:58 PM
To: Stojaczyk, DariuszX <dariuszx.stojac...@intel.com>; dev@dpdk.org
Cc: sta...@dpdk.org
Subject: Re: [PATCH] memory: fix alignment in eal_get_virtual_area()
On 13-Jun-18 8:08 PM, Dariusz Stojaczyk wrote:
Although the alignment mechanism works as intended, the `no_align`
bool flag was set incorrectly. We were aligning buffers that didn't
need extra alignment, and weren't aligning ones that really needed
it.
Fixes: b7cc54187ea4 ("mem: move virtual area function in common
directory")
Cc: anatoly.bura...@intel.com
Cc: sta...@dpdk.org
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojac...@intel.com>
---
lib/librte_eal/common/eal_common_memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/librte_eal/common/eal_common_memory.c
b/lib/librte_eal/common/eal_common_memory.c
index 4f0688f..a7c89f0 100644
--- a/lib/librte_eal/common/eal_common_memory.c
+++ b/lib/librte_eal/common/eal_common_memory.c
@@ -70,7 +70,7 @@ eal_get_virtual_area(void *requested_addr, size_t
*size,
* system page size is the same as requested page size.
*/
no_align = (requested_addr != NULL &&
- ((uintptr_t)requested_addr & (page_sz - 1)) == 0) ||
+ ((uintptr_t)requested_addr & (page_sz - 1))) ||
page_sz == system_page_sz;
do {
This patch is wrong - no alignment should be performed if address is
already alighed, e.g. if requested_addr & (page_sz - 1) == 0. The
original code was correct.
If we provide an aligned address with ADDR_IS_HINT flag and OS decides not
to use it, we end up with potentially unaligned address that needs to be
manually aligned and that's what this patch does. If the requested address
wasn't aligned to the provided page_sz, why would we bother aligning it
manually?
no_align is a flag that indicates whether we should or shouldn't align the
resulting end address - it is not meant to align requested address.
If requested_addr was NULL, no_align will be set to "false" (we don't know what
we get, so we must reserve additional space for alignment purposes).
However, it will be set to "true" if page size is equal to system size (the OS
will
return pointer that is already aligned to system page size, so we don't need to
align the result and thus don't need to reserve additional space for alignment).
If requested address wasn't null, again we don't need alignment if system page
size is equal to requested page size, as any resulting address will be already
page-aligned (hence no_align set to "true").
If requested address wasn't already page-aligned and page size is not equal to
system page size, then we set "no_align" to false, because we will need to align
the resulting address.
The crucial part to understand is that the logic here is inverted - "if
requested
address isn't NULL, and if the requested address is already aligned (i.e. (addr
&
pgsz-1) == 0), then we *don't* need to align the address". So, if the requested
address is *not* aligned, "no_align" must be set to false - because we *will*
need to align the address.
As an added bonus, we have regression testing identifying this patch as cause
for
numerous regressions :)
Yes, we have met many mulit-process related issues(hang, block) due to the
patches,
so that RC1's quality is impacted by this patch seriously.
How about current fix plan? It's a little urgent. Thx.
Hi Qian,
I've sent a patch to fix this:
http://patches.dpdk.org/project/dpdk/list/?series=607
It was already tested by Lei, but you're welcome to pile on :)
--
Thanks,
Anatoly
