linux-kernel - RE: [PATCH v2 4/5] HID: hv: Remove dependencies on PAGE

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Message-ID: <87ftoc7gd4.fsf@vitty.brq.redhat.com>
Date:   Fri, 14 Jun 2019 09:53:11 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
        "m.maya.nakamura" <m.maya.nakamura@...il.com>
Cc:     "x86\@kernel.org" <x86@...nel.org>,
        "linux-hyperv\@vger.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal\@kernel.org" <sashal@...nel.org>
Subject: RE: [PATCH v2 4/5] HID: hv: Remove dependencies on PAGE_SIZE for ring buffer

Michael Kelley <mikelley@...rosoft.com> writes:

> From: Vitaly Kuznetsov <vkuznets@...hat.com> Sent: Wednesday, June 12, 2019 3:40 AM
>> Maya Nakamura <m.maya.nakamura@...il.com> writes:
>> 
>> > Define the ring buffer size as a constant expression because it should
>> > not depend on the guest page size.
>> >
>> > Signed-off-by: Maya Nakamura <m.maya.nakamura@...il.com>
>> > ---
>> >  drivers/hid/hid-hyperv.c | 4 ++--
>> >  1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
>> > index d3311d714d35..e8b154fa38e2 100644
>> > --- a/drivers/hid/hid-hyperv.c
>> > +++ b/drivers/hid/hid-hyperv.c
>> > @@ -112,8 +112,8 @@ struct synthhid_input_report {
>> >
>> >  #pragma pack(pop)
>> >
>> > -#define INPUTVSC_SEND_RING_BUFFER_SIZE		(10*PAGE_SIZE)
>> > -#define INPUTVSC_RECV_RING_BUFFER_SIZE		(10*PAGE_SIZE)
>> > +#define INPUTVSC_SEND_RING_BUFFER_SIZE		(40 * 1024)
>> > +#define INPUTVSC_RECV_RING_BUFFER_SIZE		(40 * 1024)
>> >
>> 
>> My understanding is that this size is pretty arbitrary and as I see you
>> use it for hyperv-keyboard.c as well. It may make sense to have a
>> define, something like HYPERV_STD_RINGBUFFER_SIZE.
>
> Yes, the size is pretty arbitrary because it hasn't been important enough
> from a memory consumption or performance standpoint to run experiments
> to see if a smaller value could be used.  That said, I would not want to
> link these two devices (keyboard and mouse) by using a shared ring buffer
> size definition.  Logically, the ring buffer sizes are independent of each other,
> and using a common #define implies that they are somehow linked.

Ok, makes sense, let's keep them separate.

-- 
Vitaly