LVM: Update paragraph on multi-queue schedulers.

The single queue schedulers are history, so replace the text which
said that they are about to be replaced.

diff --git a/LVM.m4 b/LVM.m4
index abd8243c13259ca77081d76e890108ca29c04c43..959d4cec09a9ca53ef395c7926880527d66c36aa 100644 (file)
--- a/LVM.m4
+++ b/LVM.m4
@@ -60,21 +60,18 @@ they can be submitted as a unit for performance reasons. The thusly
 processed bios then form an I/O request which is handed to an <em>
 I/O scheduler </em> (also known as <em> elevator</em>). </p>
 
-<p> At this time of writing (2018-11) there exist two different sets
-of schedulers: the traditional single-queue schedulers and the
-modern multi-queue schedulers, which are expected to replace the
-single-queue schedulers soon. The three single-queue schedulers,
-noop, deadline and cfq (complete fair queueing), were designed for
-rotating disks. They reorder requests with the aim to minimize seek
-time. The newer multi-queue schedulers, mq-deadline, kyber, and bfq
-(budget fair queueing), aim to max out even the fastest devices. As
-implied by the name "multi-queue", they implement several request
-queues, the number of which depends on the hardware in use. This
-has become necessary because modern storage hardware allows multiple
-requests to be submitted in parallel from different CPUs. Moreover,
-with many CPUs the locking overhead required to put a request into
-a queue increases. Per-CPU queues allow for per-CPU locks, which
-decreases queue lock contention. </p>
+<p> Traditionally, the schedulers were designed for rotating disks.
+They implemented a single request queue and reordered the queued
+I/O requests with the aim to minimize disk seek times. The newer
+multi-queue schedulers mq-deadline, kyber, and bfq (budget fair
+queueing) aim to max out even the fastest devices. As implied by
+the name "multi-queue", they implement several request queues,
+the number of which depends on the hardware in use. This has become
+necessary because modern storage hardware allows multiple requests
+to be submitted in parallel from different CPUs. Moreover, with many
+CPUs the locking overhead required to put a request into a queue
+increases. Per-CPU queues allow for per-CPU locks, which decreases
+queue lock contention. </p>
 
 <p> We will take a look at some aspects of the Linux block layer and on
 the various I/O schedulers. An exercise on loop devices enables the