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Date: Tue, 25 Feb 2014 02:48:42 +0300
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Jerome Marchand <jmarchan@...hat.com>,
Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 4/6] zram: add multi stream functionality
On (02/25/14 08:43), Minchan Kim wrote:
> On Fri, Feb 21, 2014 at 02:50:41PM +0300, Sergey Senozhatsky wrote:
> > This patch implements multi stream compression support.
> >
> > Introduce struct zcomp_strm_multi and a set of functions to manage
> > zcomp_strm stream access. zcomp_strm_multi has a list of idle zcomp_strm
> > structs, spinlock to protect idle list and wait queue, making it possible
> > to perform parallel compressions.
> >
> > The following set of functions added:
> > - zcomp_strm_multi_get()/zcomp_strm_multi_put()
> > get and put compression stream, implement required locking
> > - zcomp_strm_multi_create()/zcomp_strm_multi_destroy()
> > create and destroy zcomp_strm_multi
> >
> > zcomp ->strm_get() and ->strm_put() callbacks are set during initialisation
> > to zcomp_strm_multi_get()/zcomp_strm_multi_put() correspondingly.
> >
> > Each time zcomp issues a zcomp_strm_multi_get() call, the following set of
> > operations performed:
> > - spin lock strm_lock
> > - if idle list is not empty, remove zcomp_strm from idle list, spin
> > unlock and return zcomp stream pointer to caller
> > - if idle list is empty, current adds itself to wait queue. it will be
> > awaken by zcomp_strm_multi_put() caller.
> >
> > zcomp_strm_multi_put():
> > - spin lock strm_lock
> > - add zcomp stream to idle list
> > - spin unlock, wake up sleeper
> >
> > Minchan Kim reported that spinlock-based locking scheme has demonstrated a
> > severe perfomance regression for single compression stream case, comparing
> > to mutex-based (https://lkml.org/lkml/2014/2/18/16)
> >
> > base spinlock mutex
> >
> > ==Initial write ==Initial write ==Initial write
> > records: 5 records: 5 records: 5
> > avg: 1642424.35 avg: 699610.40 avg: 1655583.71
> > std: 39890.95(2.43%) std: 232014.19(33.16%) std: 52293.96
> > max: 1690170.94 max: 1163473.45 max: 1697164.75
> > min: 1568669.52 min: 573429.88 min: 1553410.23
> > ==Rewrite ==Rewrite ==Rewrite
> > records: 5 records: 5 records: 5
> > avg: 1611775.39 avg: 501406.64 avg: 1684419.11
> > std: 17144.58(1.06%) std: 15354.41(3.06%) std: 18367.42
> > max: 1641800.95 max: 531356.78 max: 1706445.84
> > min: 1593515.27 min: 488817.78 min: 1655335.73
> > ==Random write ==Random write ==Random write
> > records: 5 records: 5 records: 5
> > avg: 1626318.29 avg: 497250.78 avg: 1695582.06
> > std: 38550.23(2.37%) std: 1405.42(0.28%) std: 9211.98
> > max: 1665839.62 max: 498585.88 max: 1703808.22
> > min: 1562141.21 min: 494526.45 min: 1677664.94
> > ==Pwrite ==Pwrite ==Pwrite
> > records: 5 records: 5 records: 5
> > avg: 1654641.25 avg: 581709.22 avg: 1641452.34
> > std: 47202.59(2.85%) std: 9670.46(1.66%) std: 38963.62
> > max: 1740682.36 max: 591300.09 max: 1687387.69
> > min: 1611436.34 min: 564324.38 min: 1570496.11
> >
> > When only one compression stream available, mutex with spin on owner tends
> > to perform much better than frequent wait_event()/wake_up(). This is why
> > single stream implemented as a special case with mutex locking.
>
> Side note:
>
> It's true for x86 but it could be changed in embedded system like ARM
> which is lower power compared to x86 and it also could depend on
> compression algorithm speed so I am thinking we need adaptive locking
> which sometime work with mutex sometime work with spinlock dynamically.
> Anyway, it is further work and I should investigate more.
>
> Most important thing is that this patchset wouldn't make any regression
> if we use mutex for single stream as default so I'm okay now.
>
>
good note.
> >
> > In order to compile this functionality ZRAM_MULTI_STREAM config option
> > required to be set, which will be introduced later.
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> > ---
> > drivers/block/zram/zcomp.c | 101 ++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 100 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> > index 9661226..41325ed 100644
> > --- a/drivers/block/zram/zcomp.c
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -12,9 +12,14 @@
> > #include <linux/slab.h>
> > #include <linux/wait.h>
> > #include <linux/sched.h>
> > +#ifdef CONFIG_ZRAM_MULTI_STREAM
> > +#include <linux/spinlock.h>
> > +#endif
>
> Do we really need to include spinlock.h?
not really. and I'm also droping CONFIG_ZRAM_MULTI_STREAM
ifdefs.
> >
> > #include "zcomp.h"
> >
> > +extern struct zcomp_backend zcomp_lzo;
> > +
> > /*
> > * single zcomp_strm backend private part
> > */
> > @@ -23,7 +28,18 @@ struct zcomp_strm_single {
> > struct zcomp_strm *zstrm;
> > };
> >
> > -extern struct zcomp_backend zcomp_lzo;
> > +#ifdef CONFIG_ZRAM_MULTI_STREAM
> > +/*
> > + * multi zcomp_strm backend private part
> > + */
> > +struct zcomp_strm_multi {
> > + /* protect strm list */
> > + spinlock_t strm_lock;
> > + /* list of available strms */
> > + struct list_head idle_strm;
> > + wait_queue_head_t strm_wait;
> > +};
> > +#endif
> >
> > static struct zcomp_backend *find_backend(const char *compress)
> > {
> > @@ -63,6 +79,89 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> > return zstrm;
> > }
> >
> > +#ifdef CONFIG_ZRAM_MULTI_STREAM
> > +/*
> > + * get existing idle zcomp_strm or wait until other process release
> > + * (zcomp_strm_put()) one for us
> > + */
> > +static struct zcomp_strm *zcomp_strm_multi_get(struct zcomp *comp)
> > +{
> > + struct zcomp_strm_multi *zp = comp->private;
>
> How about comp->stream instead of private?
ok. so I'll rename zcomp private in this and previous (factor out single
stream) patch
> Other than that, Looks good to me.
>
> > + struct zcomp_strm *zstrm;
> > +
> > + while (1) {
> > + spin_lock(&zp->strm_lock);
> > + if (list_empty(&zp->idle_strm)) {
> > + spin_unlock(&zp->strm_lock);
> > + wait_event(zp->strm_wait,
> > + !list_empty(&zp->idle_strm));
> > + continue;
> > + }
> > +
> > + zstrm = list_entry(zp->idle_strm.next,
> > + struct zcomp_strm, list);
> > + list_del(&zstrm->list);
> > + spin_unlock(&zp->strm_lock);
> > + break;
> > + }
> > + return zstrm;
> > +}
> > +
> > +/* add zcomp_strm back to idle list and wake up waiter */
> > +static void zcomp_strm_multi_put(struct zcomp *comp, struct zcomp_strm *zstrm)
> > +{
> > + struct zcomp_strm_multi *zp = comp->private;
> > +
> > + spin_lock(&zp->strm_lock);
> > + list_add(&zstrm->list, &zp->idle_strm);
> > + spin_unlock(&zp->strm_lock);
> > +
> > + wake_up(&zp->strm_wait);
> > +}
> > +
> > +static void zcomp_strm_multi_destroy(struct zcomp *comp)
> > +{
> > + struct zcomp_strm_multi *zp = comp->private;
> > + struct zcomp_strm *zstrm;
> > + while (!list_empty(&zp->idle_strm)) {
> > + zstrm = list_entry(zp->idle_strm.next,
> > + struct zcomp_strm, list);
> > + list_del(&zstrm->list);
> > + zcomp_strm_free(comp, zstrm);
> > + }
> > + kfree(zp);
> > +}
> > +
> > +static int zcomp_strm_multi_create(struct zcomp *comp, int num_strm)
> > +{
> > + int i;
> > + struct zcomp_strm *zstrm;
> > + struct zcomp_strm_multi *zp;
> > +
> > + comp->destroy = zcomp_strm_multi_destroy;
> > + comp->strm_get = zcomp_strm_multi_get;
> > + comp->strm_put = zcomp_strm_multi_put;
> > + zp = kmalloc(sizeof(struct zcomp_strm_multi), GFP_KERNEL);
> > + comp->private = zp;
> > + if (!zp)
> > + return -ENOMEM;
> > +
> > + spin_lock_init(&zp->strm_lock);
> > + INIT_LIST_HEAD(&zp->idle_strm);
> > + init_waitqueue_head(&zp->strm_wait);
> > +
> > + for (i = 0; i < num_strm; i++) {
> > + zstrm = zcomp_strm_alloc(comp);
> > + if (!zstrm) {
> > + zcomp_strm_multi_destroy(comp);
> > + return -ENOMEM;
> > + }
> > + list_add(&zstrm->list, &zp->idle_strm);
> > + }
> > + return 0;
> > +}
> > +#endif
> > +
> > static struct zcomp_strm *zcomp_strm_single_get(struct zcomp *comp)
> > {
> > struct zcomp_strm_single *zp = comp->private;
> > --
> > 1.9.0.291.g027825b
> >
> > --
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>
> --
> Kind regards,
> Minchan Kim
>
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