Re: [PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of sgx_reclaim_pages()

From: Dave Hansen <dave.hansen@intel.com>
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>
Subject: Re: [PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of sgx_reclaim_pages()
Date: Fri, 2 Dec 2022 14:37:09 -0800	[thread overview]
Message-ID: <47799f29-8856-8c87-240b-0667f74a3be8@intel.com> (raw)
In-Reply-To: <307b43aa5908c489913110287044e611f574db0a.camel@linux.intel.com>

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.