Re: [PATCH ipmi/kcs_bmc v1] ipmi: kcs_bmc: optimize the data buffers allocation

[Wang, Haiyue]

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@xxxxxxxxxxxxxxx>
> > ---
> > Â drivers/char/ipmi/kcs_bmc.c | 10 ++++++----
> > Â 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 = {
> > Â struct kcs_bmc *kcs_bmc_alloc(struct device *dev, int sizeof_priv, 
> > u32 channel)
> > Â {
> > ÂÂÂÂÂ struct kcs_bmc *kcs_bmc;
> > +ÂÂÂ void *buf;
> > Â ÂÂÂÂÂ kcs_bmc = devm_kzalloc(dev, sizeof(*kcs_bmc) + sizeof_priv, 
> > GFP_KERNEL);
> > ÂÂÂÂÂ if (!kcs_bmc)
> > @@ -448,11 +449,12 @@ struct kcs_bmc *kcs_bmc_alloc(struct device 
> > *dev, int sizeof_priv, u32 channel)
> > ÂÂÂÂÂ mutex_init(&kcs_bmc->mutex);
> > ÂÂÂÂÂ init_waitqueue_head(&kcs_bmc->queue);
> > Â -ÂÂÂ kcs_bmc->data_in = devm_kmalloc(dev, KCS_MSG_BUFSIZ, GFP_KERNEL);
> > -ÂÂÂ kcs_bmc->data_out = devm_kmalloc(dev, KCS_MSG_BUFSIZ, GFP_KERNEL);
> > -ÂÂÂ kcs_bmc->kbuffer = devm_kmalloc(dev, KCS_MSG_BUFSIZ, GFP_KERNEL);
> > -ÂÂÂ if (!kcs_bmc->data_in || !kcs_bmc->data_out || !kcs_bmc->kbuffer)
> > +ÂÂÂ buf = devm_kmalloc_array(dev, 3, KCS_MSG_BUFSIZ, GFP_KERNEL);
> > +ÂÂÂ if (!buf)
> > ÂÂÂÂÂÂÂÂÂ return NULL;
> > + kcs_bmc->data_in = buf;
> > +ÂÂÂ kcs_bmc->data_out = buf + KCS_MSG_BUFSIZ;
> > + kcs_bmc->kbuffer = buf + KCS_MSG_BUFSIZ * 2;
> > Â ÂÂÂÂÂ kcs_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
> > ÂÂÂÂÂ kcs_bmc->miscdev.name = dev_name(dev);