linux-kernel - [1/3] x86: Update DEBUG_TLBFLUSH options description.

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Message-Id: <20190410224449.10877-2-atish.patra@wdc.com>
Date:   Wed, 10 Apr 2019 15:44:47 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Borislav Petkov <bp@...en8.de>, Gary Guo <gary@...yguo.net>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        linux-riscv@...ts.infradead.org,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
Subject: [1/3] x86: Update DEBUG_TLBFLUSH options description.

CONFIG_DEBUG_TLBFLUSH was added in 'commit 3df3212f9722 ("x86/tlb: add
tlb_flushall_shift knob into debugfs")' to support tlb_flushall_shift
knob. The knob was removed in 'commit e9f4e0a9fe27 ("x86/mm: Rip out
complicated, out-of-date, buggy TLB flushing")'.  However, the debug
option was never removed from Kconfig. It was reused in commit
'9824cf9753ec ("mm: vmstats: tlb flush counters")' but the commit text was
never updated accordingly.

Update the Kconfig option description as per its current usage.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/x86/Kconfig.debug | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 15d0fbe27872..c1a48d4ffebb 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -125,21 +125,12 @@ config DOUBLEFAULT
 	  hair.
 
 config DEBUG_TLBFLUSH
-	bool "Set upper limit of TLB entries to flush one-by-one"
+	bool "Save tlb flush statstics to vmstat"
 	depends on DEBUG_KERNEL
 	---help---
 
-	X86-only for now.
-
-	This option allows the user to tune the amount of TLB entries the
-	kernel flushes one-by-one instead of doing a full TLB flush. In
-	certain situations, the former is cheaper. This is controlled by the
-	tlb_flushall_shift knob under /sys/kernel/debug/x86. If you set it
-	to -1, the code flushes the whole TLB unconditionally. Otherwise,
-	for positive values of it, the kernel will use single TLB entry
-	invalidating instructions according to the following formula:
-
-	flush_entries <= active_tlb_entries / 2^tlb_flushall_shift
+	Add tlbflush statstics to vmstat. It is really helpful understand tlbflush
+	performance and behavior. It should be enabled only for debugging purpose.
 
 	If in doubt, say "N".
 
-- 
2.21.0