linux-kernel - Re: [PATCH 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently

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Message-ID: <88a76cb8-2484-818a-2be6-d06a4ffef107@intel.com>
Date:   Tue, 25 Jun 2019 20:00:37 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nadav Amit <namit@...are.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently

On 6/25/19 7:35 PM, Nadav Amit wrote:
>>> 	const struct flush_tlb_info *f = info;
>>> +	enum tlb_flush_reason reason;
>>> +
>>> +	reason = (f->mm == NULL) ? TLB_LOCAL_SHOOTDOWN : TLB_LOCAL_MM_SHOOTDOWN;
>>
>> Should we just add the "reason" to flush_tlb_info?  It's OK-ish to imply
>> it like this, but seems like it would be nicer and easier to track down
>> the origins of these things if we did this at the caller.
> 
> I prefer not to. I want later to inline flush_tlb_info into the same
> cacheline that holds call_function_data. Increasing the size of
> flush_tlb_info for no good reason will not help…

Well, flush_tlb_info is at 6/8ths of a cacheline at the moment.
call_function_data is 3/8ths.  To me, that means we have some slack in
the size.