linux-kernel - Re: [PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of sgx_reclaim

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Date:   Fri, 02 Dec 2022 14:17:33 -0800
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>, jarkko@...nel.org,
        dave.hansen@...ux.intel.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     zhiquan1.li@...el.com, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of
 sgx_reclaim_pages()

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/