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SubjectRe: [PATCH 1/6] firewire: core: reduce stack usage in bus reset tasklet
Stefan Richter wrote:
> pageexec@freemail.hu wrote:
>> On 6 Sep 2009 at 18:48, Stefan Richter wrote:
>>
>>> Index: linux-2.6.31-rc9/drivers/firewire/core-card.c
>>> ===================================================================
>>> --- linux-2.6.31-rc9.orig/drivers/firewire/core-card.c
>>> +++ linux-2.6.31-rc9/drivers/firewire/core-card.c
>>> @@ -38,16 +38,21 @@
>>>
>>> #include "core.h"
>>>
>>> -int fw_compute_block_crc(u32 *block)
>>> +int fw_compute_block_crc(u32 *block, gfp_t flags)
>>> {
>>> - __be32 be32_block[256];
>>> - int i, length;
>>> + static __be32 *be32_block;
>> ^^^^^^
>>
>> did you actually mean that to be static? if so, then you might as well
>> allocate the
>> buffer statically and not worry about a runtime allocation failure.
>
> Uh, that's a cut'n'paste mistake. It shouldn't be static. Thanks, I'll
> correct that before I put it into linux1394-2.6.git.
>
>>> + int i, length = (*block >> 16) & 0xff;
>>> +
>>> + be32_block = kmalloc(length * 4, flags);
>>> + if (WARN_ON(!be32_block))
>>> + goto out;
>>>
>>> - length = (*block >> 16) & 0xff;
>>> for (i = 0; i < length; i++)
>>> be32_block[i] = cpu_to_be32(block[i + 1]);
>>> *block |= crc_itu_t(0, (u8 *) be32_block, length * 4);
>>>
>>> + kfree(be32_block);
>>> + out:
>>> return length;
>>> }

This can be optimized further to get rid of the temporary be32_block
entirely.

There are two users of fw_compute_block_crc: The functions which
generate the local Config ROM CSR and then pass it down to the low-level
driver, and the function which which generates the local Topology Map
CSR and stores it for core-transaction.c::handle_topology_map() to read
on demand.

The low-level driver then needs to convert the Config ROM to __be32[].
Likewise, handle_topology_map needs to convert the Topology Map to
__be32[]. They would be both better off if we stored their input as
__be32[] in the first place, and of course do so before we compute the
CRC. Duh.

I'll rewrite patch 1/6 and 5/6 accordingly.
--
Stefan Richter
-=====-==--= =--= --===
http://arcgraph.de/sr/


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