Re: [PATCH 3/5] IB/hfi1: Adjust another size determination in hfi1_user_sdma_alloc_queues()

From: Johannes Thumshirn
Date: Mon Feb 13 2017 - 04:52:01 EST

On 02/13/2017 10:32 AM, SF Markus Elfring wrote:
>>> @@ -443,8 +442,8 @@ int hfi1_user_sdma_alloc_queues(struct hfi1_ctxtdata *uctxt, struct file *fp)
>>> if (!cq)
>>> goto cq_nomem;
>>> - memsize = PAGE_ALIGN(sizeof(*cq->comps) * hfi1_sdma_comp_ring_size);
>>> - cq->comps = vmalloc_user(memsize);
>>> + cq->comps = vmalloc_user(PAGE_ALIGN(sizeof(*cq->comps)
>>> + * hfi1_sdma_comp_ring_size));
>>> if (!cq->comps)
>>> goto cq_comps_nomem;
>> IMHO this makes readability worse.
> How often does it really make sense to keep such a product in this local variable?

It depends. Lets take it the other way round. If I this in a review I'd
suggest the submitter to create a local variable for the multiplication
to get rid of the line break. It's avoidable. And again, the compiler
will optimize it away.

Apart from the fact that you haven't tested your patch at all:

jthumshirn@linux-x5ow:linux (test)$ git am ~/\[PATCH\ 3_5\]\ IB_hfi1\:\
Adjust\ another\ size\ determination\ in\
Applying: IB/hfi1: Adjust another size determination in
jthumshirn@linux-x5ow:linux (test)$ make
drivers/infiniband/hw/hfi1/user_sdma.o CHK
CHK include/generated/uapi/linux/version.h
CHK include/generated/utsrelease.h
CHK include/generated/bounds.h
CHK include/generated/timeconst.h
CHK include/generated/asm-offsets.h
CALL scripts/
CC drivers/infiniband/hw/hfi1/user_sdma.o
drivers/infiniband/hw/hfi1/user_sdma.c: In function
drivers/infiniband/hw/hfi1/user_sdma.c:402:2: error: âmemsizeâ
undeclared (first use in this function)
memsize = sizeof(*pq->reqs) * hfi1_sdma_comp_ring_size;
drivers/infiniband/hw/hfi1/user_sdma.c:402:2: note: each undeclared
identifier is reported only once for each function it appears in
scripts/ recipe for target
'drivers/infiniband/hw/hfi1/user_sdma.o' failed
make[1]: *** [drivers/infiniband/hw/hfi1/user_sdma.o] Error 1
Makefile:1640: recipe for target
'drivers/infiniband/hw/hfi1/user_sdma.o' failed
make: *** [drivers/infiniband/hw/hfi1/user_sdma.o] Error 2

With this fixed:

jthumshirn@linux-x5ow:linux (test)$ size
text data bss dec hex filename
15393 212 292 15897 3e19
15393 212 292 15897 3e19

Glancing over the diff of the objdump of these two object files you'll
notice that all your patch is doing is moving the code around in the
.text section of the binary.

So to sum up: there is no evident improvement in the resulting binary
and you introduce a stylistic glitch (the new line break in a function

But all of what I've provided above would have been your job as patch
submitter. You have to reason why your patch is good, it's not our job
to reason why it's bad.


Johannes Thumshirn Storage
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