linux-kernel - Re: [RFC PATCH 01/20] x86/sgx: Call cond_resched() at the end of sgx_reclaim

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Message-ID: <Yy2oeiafoe1Cxz9C@kernel.org>
Date:   Fri, 23 Sep 2022 15:37:14 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH 01/20] x86/sgx: Call cond_resched() at the end of
 sgx_reclaim_pages()

On Fri, Sep 23, 2022 at 03:35:25PM +0300, Jarkko Sakkinen wrote:
> On Fri, Sep 23, 2022 at 03:32:43PM +0300, Jarkko Sakkinen wrote:
> > On Thu, Sep 22, 2022 at 10:10:38AM -0700, Kristen Carlson Accardi wrote:
> > > From: Sean Christopherson <sean.j.christopherson@...el.com>
> > > 
> > > Move the invocation of post-reclaim cond_resched() from the callers of
> > > sgx_reclaim_pages() into the reclaim path itself.   sgx_reclaim_pages()
> > > is always called in a loop and is always followed by a call to
> > > cond_resched().  This will hold true for the EPC cgroup as well, which
> > > adds even more calls to sgx_reclaim_pages() and thus cond_resched().
> > 
> > This would be in my opinion better:
> > 
> > "
> > In order to avoid repetion of cond_sched() in ksgxd() and
> > sgx_alloc_epc_page(), move the call inside sgx_reclaim_pages().
> > 
> > This will hold true for the EPC cgroup as well, which adds more
> > call sites sgx_reclaim_pages().
> > "
> > 
> > This way it is dead obvious and is better description because
> > it enumerates the consequences (i.e. call sites).
> 
> Forgot 3rd call site: sgx_reclaim_direct(), which is used by
> SGX2 ioctls. The call sites of sgx_reclaim_direct() do not
> call cond_resched(). You should address why adding this call
> to those flows is fine.

Ofc adding a parameter to sgx_reclaim_pages() for cond_resched() call is
other option (not emphasising either option).

BR, Jarkko