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Subject: Re: [PATCH ipmi/kcs_bmc v1] ipmi: kcs_bmc: optimize the data buffers
 allocation
From:   "Wang, Haiyue" <haiyue.wang@linux.intel.com>
To:     minyard@acm.org, openipmi-developer@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
References: <1521116452-4993-1-git-send-email-haiyue.wang@linux.intel.com>
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 <dd4e07c4-7a99-3449-fd2d-58c2b829f7b7@linux.intel.com>
Message-ID: <1710edd4-277b-1d2e-5885-a070751ddd2a@linux.intel.com>
Date:   Sat, 7 Apr 2018 15:54:53 +0800
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Hi Corey,

Since IPMI 2.0 just defined minimum, no maximum:

----

KCS/SMIC Input : Required: 40 bytes IPMI Message, minimum

KCS/SMIC Output : Required: 38 bytes IPMI Message, minimum

----

We can enlarge the block size for avoiding waste, and make our driver

support most worst message size case. And I think this patch make checking

simple (from 3 to 1), and the code clean, this is the biggest reason I 
want to

change. The TLB is just memory management study from book, no data to

support access improvement. :)

BR,

Haiyue


On 2018-04-07 10:37, Wang, Haiyue wrote:
>
>
> On 2018-04-07 05:47, Corey Minyard wrote:
>> On 03/15/2018 07:20 AM, Haiyue Wang wrote:
>>> Allocate a continuous memory block for the three KCS data buffers with
>>> related index assignment.
>>
>> I'm finally getting to this.
>>
>> Is there a reason you want to do this?  In general, it's better to 
>> not try to
>> outsmart your base system.  Depending on the memory allocator, in this
>> case, you might actually use more memory.  You probably won't use any
>> less.
>>
> I got this idea from another code review, but that patch allocates 30 
> more
> the same size memory block, reducing the devm_kmalloc call will be 
> better.
> For KCS only have 3, may be the key point is memory waste.
>
>> In the original case, you allocate three 1000 byte buffers, resulting 
>> in 3
>> 1024 byte slab allocated.
>>
>> In the changed case, you will allocate a 3000 byte buffer, resulting in
>> a single 4096 byte slab allocation, wasting 1024 more bytes of memory.
>>
> As the kcs has memory copy between in/out/kbuffer, put them in the same
> page will be better ? Such as the same TLB ? (Well, I just got this 
> from book,
> no real experience of memory accessing performance. And also, I was told
> that using space to save the time. :-)).
>
> Just my stupid thinking. I'm OK to drop this patch if it doesn't help 
> with
> performance, or something else.
>
> BR.
> Haiyue
>
>> -corey
>>
>>> Signed-off-by: Haiyue Wang <haiyue.wang@linux.intel.com>
>>> ---
>>>   drivers/char/ipmi/kcs_bmc.c | 10 ++++++----
>>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/char/ipmi/kcs_bmc.c b/drivers/char/ipmi/kcs_bmc.c
>>> index fbfc05e..dc19c0d 100644
>>> --- a/drivers/char/ipmi/kcs_bmc.c
>>> +++ b/drivers/char/ipmi/kcs_bmc.c
>>> @@ -435,6 +435,7 @@ static const struct file_operations kcs_bmc_fops 
>>> = {
>>>   struct kcs_bmc *kcs_bmc_alloc(struct device *dev, int sizeof_priv, 
>>> u32 channel)
>>>   {
>>>       struct kcs_bmc *kcs_bmc;
>>> +    void *buf;
>>>         kcs_bmc = devm_kzalloc(dev, sizeof(*kcs_bmc) + sizeof_priv, 
>>> GFP_KERNEL);
>>>       if (!kcs_bmc)
>>> @@ -448,11 +449,12 @@ struct kcs_bmc *kcs_bmc_alloc(struct device 
>>> *dev, int sizeof_priv, u32 channel)
>>>       mutex_init(&kcs_bmc->mutex);
>>>       init_waitqueue_head(&kcs_bmc->queue);
>>>   -    kcs_bmc->data_in = devm_kmalloc(dev, KCS_MSG_BUFSIZ, 
>>> GFP_KERNEL);
>>> -    kcs_bmc->data_out = devm_kmalloc(dev, KCS_MSG_BUFSIZ, GFP_KERNEL);
>>> -    kcs_bmc->kbuffer = devm_kmalloc(dev, KCS_MSG_BUFSIZ, GFP_KERNEL);
>>> -    if (!kcs_bmc->data_in || !kcs_bmc->data_out || !kcs_bmc->kbuffer)
>>> +    buf = devm_kmalloc_array(dev, 3, KCS_MSG_BUFSIZ, GFP_KERNEL);
>>> +    if (!buf)
>>>           return NULL;
>>> +    kcs_bmc->data_in  = buf;
>>> +    kcs_bmc->data_out = buf + KCS_MSG_BUFSIZ;
>>> +    kcs_bmc->kbuffer  = buf + KCS_MSG_BUFSIZ * 2;
>>>         kcs_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
>>>       kcs_bmc->miscdev.name = dev_name(dev);
>>
>>
>