Message-ID: <6bdd805d-6a99-a1d5-f376-3d2d0c915d38@collabora.com>
Date:   Mon, 20 Feb 2023 12:15:31 +0500
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Cc:     Muhammad Usama Anjum <usama.anjum@collabora.com>,
        David Hildenbrand <david@redhat.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Nadav Amit <nadav.amit@gmail.com>
Subject: Re: [PATCH] mm/uffd: UFFD_FEATURE_WP_ZEROPAGE
To:     Peter Xu <peterx@redhat.com>
References: <20230215210257.224243-1-peterx@redhat.com>
 <7eb2bce9-d0b1-a0e3-8be3-f28d858a61a0@redhat.com> <Y+5Z+88Z3T2TyxUI@x1n>
 <4f64d62f-c21d-b7c8-640e-d41742bbbe7b@redhat.com> <Y+5uIS5E9sTLi41T@x1n>
 <456f8e2e-9554-73a3-4fdb-be21f9cc54b6@redhat.com> <Y+6NKPuty9V3nycI@x1n>
 <427298c4-0da9-059f-02ff-c5147d317c87@collabora.com> <Y/AJUi4o5hOKDkgy@x1n>
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From:   Muhammad Usama Anjum <usama.anjum@collabora.com>
In-Reply-To: <Y/AJUi4o5hOKDkgy@x1n>
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Hi Peter,

Thank you so much for working on this.

On 2/18/23 4:10 AM, Peter Xu wrote:
> Hi, Muhammad,
> 
> On Fri, Feb 17, 2023 at 05:31:19PM +0500, Muhammad Usama Anjum wrote:
>> I've just ran my single threaded selftest [1] over an over again to get
>> some numbers.
>>
>> Without zeropage
>> qemu has 6 cores: 26.0355
> 
> Did you count in the time of read prefault?  Or did you not prefault at
> all?
No, pre-faulting is not being done in both of the runs.

Without zeropage, I'm checking pte_none() to decide if page is dirty.
With zeropage, I'm just checking if WP flag isn't set to decide if page is
dirty.

> 
>> With zeropage
>> qemu has 6 cores: 39.203
>>
>> 33% worse performance with zero pages
>>
>> Definitely, there can be better benchmark application. Please let me know
>> if I should write better benchmarks on my end.
>>
>> [1]
>> https://lore.kernel.org/all/20230202112915.867409-7-usama.anjum@collabora.com
> 
> I'll have a closer look too next week.
> 
> Thanks,
> 

-- 
BR,
Muhammad Usama Anjum