On Sat, Aug 24, 2024 at 12:17:57PM -0500, Segher Boessenkool wrote:
> > Are these functions also used on DMA coherent memory ?
>
> Most won't show up high on most profiles, heh. Which you already
> can see from the problem not being attacked yet: if it was so obviously
> a problem, some people wo
On Sat, Aug 24, 2024 at 09:01:33AM +, LEROY Christophe wrote:
> Le 23/08/2024 à 21:19, Segher Boessenkool a écrit :
> > The memset() code itself could chech for the storage attributes, but
> > that is probably more expensive than just assuming the happy case.
> > Maybe someone could try it out
Le 23/08/2024 à 21:19, Segher Boessenkool a écrit :
> ***ATTENTION, Sopra Steria Group cannot confirm the identity of this email
> sender (SPF record failure). This might be a fake email from an attacker, if
> you have any doubts report and delete the email.***
>
> ***ATTENTION, Sopra Steria G
On 8/23/24 9:19 PM, Segher Boessenkool wrote:
Hi!
On Fri, Aug 23, 2024 at 03:54:59PM +0200, Christoph Hellwig wrote:
On Fri, Aug 23, 2024 at 08:06:00AM -0500, Segher Boessenkool wrote:
What does "uncached memory" even mean here? Literally it would be
I=1 memory (uncachEABLE memory), but more
Hi!
On Fri, Aug 23, 2024 at 03:54:59PM +0200, Christoph Hellwig wrote:
> On Fri, Aug 23, 2024 at 08:06:00AM -0500, Segher Boessenkool wrote:
> > What does "uncached memory" even mean here? Literally it would be
> > I=1 memory (uncachEABLE memory), but more likely you want M=0 memory
> > here ("no
On Fri, Aug 23, 2024 at 08:06:00AM -0500, Segher Boessenkool wrote:
> What does "uncached memory" even mean here? Literally it would be
> I=1 memory (uncachEABLE memory), but more likely you want M=0 memory
> here ("non-memory memory", "not well-behaved memory", MMIO often).
Regular kernel memory
Hi!
On Thu, Aug 22, 2024 at 06:39:33AM +, LEROY Christophe wrote:
> Le 22/08/2024 à 07:32, Christoph Hellwig a écrit :
> > On Thu, Aug 22, 2024 at 05:25:10AM +, LEROY Christophe wrote:
> >>> and this results in a call to dma_direct_allocation(), which has one
> >>> innocent looking memset(
dma_alloc_from_pool is the allocator used when the caller can't
sleep, and as that is reusing memory it really has to call memset
or a memset-like function on the already uncached memory
unfortunately. The dma engine operation that is doing this allocation
is documented as not being able to sleep,
Hi!
Thank you all for your insightful insights :-) .
... and derp, used the wrong mail.
On 8/22/24 9:14 AM, Christoph Hellwig wrote:
On Thu, Aug 22, 2024 at 06:39:33AM +, LEROY Christophe wrote:
powerpc has a magic instruction 'dcbz' which clears a full cacheline in
one go. It is far more
On Thu, 2024-08-22 at 09:14 +0200, Christoph Hellwig wrote:
>
> I'd suggest two things:
>
> 1) remove the warning. The use case is perfectly valid and everything
> using uncached memory is already slow, so people will just have to
> deal with it. Maybe offer a trace point instead if pe
On Thu, Aug 22, 2024 at 06:39:33AM +, LEROY Christophe wrote:
> powerpc has a magic instruction 'dcbz' which clears a full cacheline in
> one go. It is far more efficient than a loop to store zeros, and since
> 2015 memset(0) has been implemented with that instruction (commit
> 5b2a32e80634
Le 22/08/2024 à 07:32, Christoph Hellwig a écrit :
> On Thu, Aug 22, 2024 at 05:25:10AM +, LEROY Christophe wrote:
>>> and this results in a call to dma_direct_allocation(), which has one
>>> innocent looking memset():
>>
>>
>> memset() can't be used on non-cached memory, memset_io() has to b
On Thu, Aug 22, 2024 at 05:25:10AM +, LEROY Christophe wrote:
> > and this results in a call to dma_direct_allocation(), which has one
> > innocent looking memset():
>
>
> memset() can't be used on non-cached memory, memset_io() has to be used
> instead.
No, we use memset on uncached memory
+ CC Christoph Hellwig
Hi,
Le 22/08/2024 à 00:39, Christian Lamparter a écrit :
> [Vous ne recevez pas souvent de courriers de
> christian.lampar...@isd.uni-stuttgart.de. Découvrez pourquoi ceci est
> important à https://aka.ms/LearnAboutSenderIdentification ]
>
> Sorry to write a reply to this o
Sorry to write a reply to this old mail. But after years, I finally
decided to tackle an "old" problem that has come up...
And unfortunately it is related to this patch. But let me explain.
On 9/16/21 4:52 PM, Christophe Leroy wrote:
dcbz instruction shouldn't be used on non-cached memory. Using
On Thu, 16 Sep 2021 16:52:09 +0200, Christophe Leroy wrote:
> dcbz instruction shouldn't be used on non-cached memory. Using
> it on non-cached memory can result in alignment exception and
> implies a heavy handling.
>
> Instead of silentely emulating the instruction and resulting in high
> perfor
dcbz instruction shouldn't be used on non-cached memory. Using
it on non-cached memory can result in alignment exception and
implies a heavy handling.
Instead of silentely emulating the instruction and resulting in high
performance degradation, warn whenever an alignment exception is
taken in kern
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