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Message-ID: <307b43aa5908c489913110287044e611f574db0a.camel@linux.intel.com>
Subject: Re: [PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of
 sgx_reclaim_pages()
From:   Kristen Carlson Accardi <kristen@linux.intel.com>
To:     Dave Hansen <dave.hansen@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>
Date:   Fri, 02 Dec 2022 14:17:33 -0800
In-Reply-To: <746adf31-e70c-e32d-a35d-72d352af613b@intel.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>
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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)
> > > > +{
> > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0__sgx_reclaim_pages();
> > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0cond_resched();
> > > > +}
> > > Why bother with the wrapper?=C2=A0 Can't we just put cond_resched() i=
n
> > > 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.
>=20
> 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@inte=
l.com/