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Message-ID: <47799f29-8856-8c87-240b-0667f74a3be8@intel.com>
Date:   Fri, 2 Dec 2022 14:37:09 -0800
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Subject: Re: [PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of
 sgx_reclaim_pages()
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To:     Kristen Carlson Accardi <kristen@linux.intel.com>,
        jarkko@kernel.org, dave.hansen@linux.intel.com, tj@kernel.org,
        linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org,
        cgroups@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Cc:     zhiquan1.li@intel.com, Sean Christopherson <seanjc@google.com>
References: <20221202183655.3767674-1-kristen@linux.intel.com>
 <20221202183655.3767674-2-kristen@linux.intel.com>
 <37de083d-a63b-b2ff-d00a-e890a1ba5eea@intel.com>
 <da690a45a36038399c63ddac8f0efed9872ec13e.camel@linux.intel.com>
 <746adf31-e70c-e32d-a35d-72d352af613b@intel.com>
 <307b43aa5908c489913110287044e611f574db0a.camel@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <307b43aa5908c489913110287044e611f574db0a.camel@linux.intel.com>
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On 12/2/22 14:17, Kristen Carlson Accardi wrote:
> On Fri, 2022-12-02 at 13:45 -0800, Dave Hansen wrote:
>> On 12/2/22 13:37, Kristen Carlson Accardi wrote:
>>>>> +static void sgx_reclaim_pages(void)
>>>>> +{
>>>>> +       __sgx_reclaim_pages();
>>>>> +       cond_resched();
>>>>> +}
>>>> Why bother with the wrapper?  Can't we just put cond_resched() in
>>>> the
>>>> existing sgx_reclaim_pages()?
>>> Because sgx_reclaim_direct() needs to call sgx_reclaim_pages()
>>> but not do the cond_resched(). It was this or add a boolean or
>>> something to let caller's opt out of the resched.
>>
>> Is there a reason sgx_reclaim_direct() *can't* or shouldn't call
>> cond_resched()?
> 
> Yes, it is due to performance concerns. It is explained most succinctly
> by Reinette here:
> 
> https://lore.kernel.org/linux-sgx/a4eb5ab0-bf83-17a4-8bc0-a90aaf438a8e@intel.com/

I think I'd much rather have 3 cond_resched()s in the code that
effectively self-document than one __something() in there that's a bit
of a mystery.

Everyone knows what cond_resched() means.