linux-kernel - Re: [PATCH 5/6] KVM: selftests: memslot_perf

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Date:   Mon, 17 Oct 2022 23:32:10 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        kvmarm@...ts.cs.columbia.edu, kvmarm@...ts.linux.dev,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        ajones@...tanamicro.com, pbonzini@...hat.com, maz@...nel.org,
        shuah@...nel.org, oliver.upton@...ux.dev, peterx@...hat.com,
        ricarkol@...gle.com, zhenyzha@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH 5/6] KVM: selftests: memslot_perf_test: Consolidate
 memory sizes

On Tue, Oct 18, 2022, Gavin Shan wrote:
> On 10/18/22 6:56 AM, Maciej S. Szmigiero wrote:
> > On 18.10.2022 00:51, Gavin Shan wrote:
> > > On 10/18/22 6:08 AM, Sean Christopherson wrote:
> > > > On Mon, Oct 17, 2022, Maciej S. Szmigiero wrote:
> > > > > > +#define MEM_EXTRA_SIZE        0x10000
> > > > > 
> > > > > Also, an expression like "(64 << 10)" is more readable than a "1"
> > > > > with a tail of zeroes (it's easy to add one zero too many or be one
> > > > > zero short).
> > > > 
> > > > +1 to not open coding raw numbers.
> > > > 
> > > > I think it's high time KVM selftests add #defines for the common sizes, e.g. SIZE_4KB,
> > > > 16KB, 64K, 2MB, 1GB, etc...
> > > > 
> > > > Alternatively (or in addition), just #define 1KB, 1MB, 1GB, and 1TB, and then do
> > > > math off of those.
> > > > 
> > > 
> > > Ok. I will have one separate patch to define those sizes in kvm_util_base.h,
> > > right after '#define NSEC_PER_SEC 1000000000L'. Sean, could you let me know
> > > if it looks good to you?
> > > 
> > >      #define KB         (1UL << 10)
> > >      #define MB         (1UL << 20)
> > >      #define GB         (1UL << 30)
> > >      #define TB         (1UL << 40)

Any objection to prefixing these with SIZE_ as well?  IMO it's worth burning the
extra five characters to make it all but impossible to misinterpret code.

> > >      /* Base page and huge page size */
> > >      #define SIZE_4KB   (  4 * KB)
> > >      #define SIZE_16KB  ( 16 * KB)
> > >      #define SIZE_64KB  ( 64 * KB)
> > >      #define SIZE_2MB   (  2 * MB)
> > >      #define SIZE_32MB  ( 32 * MB)
> > >      #define SIZE_512MB (512 * MB)
> > >      #define SIZE_1GB   (  1 * GB)
> > >      #define SIZE_16GB  ( 16 * GB)
> > 
> > FYI, QEMU uses KiB, MiB, GiB, etc., see [1].
> > 
> 
> Right. I checked QEMU's definitions and it makes sense to use
> KiB, MiB, GiB, TiB. I don't think we need PiB and EiB because
> our tests don't use that large memory.

Ha!  I had typed out KiB, etc... but then thought, "nah, I'm being silly".  KiB
and friends work for me.